I'll try and keep these in alphabetical order.
angled cuts: Cuts which are made at different possible angles (usually right, left, and center) to the length of the key blade.
anti-drill ball bearings/lunes/rods: Ball bearings which are built into a cylinder in front of the first pin chamber to prevent drilling of the shear line(s).
backplate: A plate on the inside of a door through which the cylinder connecting screws and tailpiece is passed.
backset: The horizontal distance from the edge of a door to the center of a lockset.
barrel key: A key with a bit projecting from a hollow cylindrical shaft.
bicentric cylinder: A lock cylinder, usually of the pin tumbler type, that has two plugs and two sets of pin chambers instead of one.
bi-lock: A pin tumber cylinder lock consisting of two parallel rows of pin tumblers and two sidebars operated by a U shaped key.
bit key: A key with a bit projecting from a solid cylindrical shaft. The bit has cuts to bypass the wards or operate levers in the correct lock.
bit key lock: A warded or lever lock that uses bit keys.
bitting: A cut, or series of cuts, on the bit or blade of a key.
blade: The portion of the key that is inserted into the lock.
blank: A key before any cuts have been made.
bolt: The part which is moved into a locked or unlocked position.
bottom pin (tumblers): Cylinder pins usually made of brass used in setting combinations pin tumbler cylinders. Varied in length and tapered at one end allows them to sit in the "v" cuts made in keys. When the proper key is inserted, the pins form a shearline allowing the plug of the lock to be turned. (Since lock orientation can vary by region, the alternate term "key pin" is preferred.)
bow: The handle of the key.
british standard lever lock, bs lock: this differs from a normal lever lock in that, it must have at least 1000 key differs, it must have anti drill plate, it must have anti saw rollers in bolt, it must be tested against crow bar attack to minimum standard, it must have a security curtain, it must have anti pick defences, ie anti pick notches or false gates, it must meet many other tests, but in short its tougher to pick and tougher to drill.
broaching: Part of the cross section of a keyway where metal has been removed.
bypass: A method of opening a lock in which the part of the mechanism that is directly operated by the key is by-passed. Carding, shimming, etc. are examples.
by-pass tool: A device that neutralizes the security of a locking device, or its application hardware, often taking advantage of a design weakness
cabinet lock: A relatively small type of lock designed to be used on drawers, cabinets, pieces of furniture, or thin doors.
cam: The part of a lock or cylinder which activates the bolt or latch as the key is turned. The cam may also act as the bolt.
cam lock: A lock that has an attached cam that serves as the lock's bolt. Cam locks are often used on cabinets, file cabinets and drawers.
case: The housing or body of a lock.
case ward: Protrusions that stick out of the sides of the keyway to allow entry of only the correct type of key blank.
change index: The point on a key changeable combination lock dial ring to which the old and new combinations must be dialed when changing the combination.
change key: The key that operates one lock in a masterkeyed system.
changeable lever: An adjustable lever consisting of a detent and sweep lever. The deten lever is unlocked from the sweep lever with a change key.
clevis: A metal link for attaching a chain to a padlock.
clover leaf cam: In certain types of mortise locks, a cylinder cam that has three lobes, instead of one, to activate the boltwork of the lock.
code: A series of numbers or digits on a key or lock that specifies or references the particular cuts of the key to operate a lock.
code key machine: A device for making a first key when its cut depth numbers and its spacing are known.
Comb pick: A comb-shaped tool which is used to lift the pin tumblers of a cylinder above their normal shear line.
control key: A key used to remove the core from an interchangeable core cylinder.
control shear line: The shear line which allows operation of the control lug of an interchangeable core.
control sleeve: The part of an interchangeable core retaining device which surrounds the plug.
cross-bore: A hole drilled into the face of a door where a bored or interconnected lockset is to be installed.
[cut depth number: A short number, usually having only one digit, which is used as a shorthand way to represent a cut depth. eg. a number 3 cut might stand for .290 of an inch.
curtain: found on lever locks, the curtain is a security barrel that restricts access to the lever pack and acts as the bolt thrower.
curtain pick: this is a form of specialist 2 in 1 pick devised to pick lever locks fitted with a curtain, it enables you to put tension on the curtain/bolt thrower and have access to lift each lever in turn .
cuts: A cut, or series of cuts, on the bit or blade of a key.
cylinder key: A key for use with pin tumbler and wafer tumbler cylinder locks.
cylindrical lockset: A bored lockset whose latch or bolt locking mechanism is contained in the portion installed through the cross-bore.
deadbolt: A lock bolt, usually rectangular, that has no spring action, and that becomes locked against end pressure when fully projected.
deadlatch: A lock with a beveled latch bolt that can be automatically or manually locked against end pressure when projected.
deadlock: A lock that projects a deadbolt.
deadlocking: Pertaining to any feature which, when fully engaged, resists attempts to move the latch or bolt in the unlocking direction through direct pressure.
deadlocking latch: A latchbolt with a deadlocking mechanism.
depth: The depth of a cut is measured from the bottom of the blade up to the bottom of a cut. Depths are numbered starting with #0 (or sometimes #1) as the highest depth.
depth key: A special key that enables a locksmith to cut blanks made from a particular lock according to a key code.
double-acting lever tumbler: One which must be lifted a precise amount, neither too little nor too much to allow movement of a bolt.
double cylinder: Pertaining to a lock with two keyed cylinders.
double cylinder deadlock: A deadbolt lock whose bolt may be operated by a key from either side.
driver (driver pin): Any pin in a pin stack that sits adjacent to a spring. In North American locks, these are commonly called "top pins".
Euro Profile Cylinder : The shape of a standard lever lock keyway in central Europe is such so that manufacturers use the same lever lock lock-case as a basis for the Euro lock cylinder. The cylinder is normally fitted with the pins "upside" down, to allow the cam on the cylinder to reach the lever lock mechanism.
Picture (Thanks to Chubby)
flat steel key: A key which is completely flat on both sides, usually used for warded or lever tumbler locks.
Follower: A small cylindrical object that is pushed behind conventional pin-tumbler cylinder cores on removal for use of rekeying. The follower is used to keep the top pins and springs in place, meaning you don't have to re-load the pins and springs every time you pull the plug out. (Thanks to Mutzy)
full mortise: Pertaining to a method of installation in which only the face plate and trim is exposed. The lock case is installed in a pocket in the door or drawer.
grooves: Long narrow milled out areas along the sides of the blade to allow the blade to bypass the wards in the keyway.
hard plate: also refered to as anti drill plate, this is a hardened steel plate placed over the drill vulnerable areas of a lock, an hss bit will not drill this, instead a hard plate drill must be used.
hasp: A hinged metal strap designed to be passed over a staple and secured in place.
heel & toe locking: Describes a padlock which has locking dogs at both the heel and toe of the shackle.
heel (of a padlock shackle): The part of a padlock shackle which is retained in the case when in the unlocked position.
hollow post key: A key with a bit projecting from a hollow cylindrical shaft.
hook bolt: A lock bolt shaped in the general outline of a hook. Normally used on sliding doors or where spreading of the frame and door is a possible attack.
impressioning: A means of fitting a key directly to a locked cylinder by manipulating a blank in the keyway and cutting the blank where the tumlbers have made marks.
impressioning kits for bs locks:these kits allow you to take an impression of a lever lock using a reader key and plastacine , you decode the impression and build a working key using the make up key and pin set.
interconnected lockset: A lockset whose trim provides a means of simultaneous retraction of two or more bolts which may also be operated independently.
jamb: The inside vertical face of a doorway.
key code: A series of numbers or digits on a key or lock that specifies or references the particular cuts of the key to operate a lock.
key pin: Any pin that makes contact with the key when inserted. Commonly referred to as "bottom pins" in North American locks.
keyway: The part of the plug where you insert the key.
keyway grooves: Long narrow milled out areas along the sides of the blade to allow the blade to bypass the wards in the keyway.
latch: A mechanical device which automatically keeps a door closed until a deliberate action is used to retract it.
lever lock: Lock with levers that are each lifted to the correct level by a bit key or flat metal key to enable the lock to operate.
lever pack: A set of lever tumblers.
lever tumbler: Usually a flat, spring-loaded tumbler which pivots on a post.
lock: Any device which prevents access or use by requiring special knowledge or equipment.
Lock Picking 101: This defines as either Lock Picking Beginners Class or Lock Picking can be your worse nightmare.
(thanks to macaba for that addition.)
locksmith: A person with the knowledge and ability to select, install, service and bypass all the components of an electrical or mechanical lock.
lower pins: The pins of a lock that contact the cuts on the key. Also called bottom pins.
MACS: Maximum Adjacent Cut Specification. Specified by the lock manufacturer, this refers to the greatest allowable difference between adjacent pin sizes. This is done to prevent possible key malfunction that could occur as a result of steep ramps on a key.
mortise cylinder: A type of lock cylinder designed to fit into a mortise lock and operate the mechanism. Typically these cylinders are threaded and screw into the lock case.
mortise lock A type of lock where the case of the lock is inside a mortised out pocket in the edge of the door.
pin stack: The combination of a lower pin sitting beneath an upper pin. In master keyed locks, additional master pins may be located between the lower and upper pins.
plug: The part of the lock that you put the key into, and which turns to operate the lock.
pre-assembled lockset: A lock designed to be installed into a cutout in the edge of a door. The lock body and most or all of its trim need no further assembly other than securing it to the door.
rim lock: A lock or latch typically mounted on the surface of a door or drawer.
shackle: The part of a padlock which passes through an opening in an object or fits around an object and is ultimately locked into the case.
shear line: The dividing line between the plug and the shell (the height to which the tops of the lower pins must be raised to open the lock).
shell: The outer part of the lock that surrounds the plug.
shimming: A process by which a lock can be dissasembled without use of an operating key.
shoulder: The edge of the key that touches the face of the lock to define how far the key is inserted into the lock.
single-acting lever tumbler: A lever tumbler which must be moved a minimum distance to allow travel of a bolt, but cannot be moved so far as to restrict travel of the bolt.
skeleton key: Any non-cylinder key whose bit, blade, and/or post is cut away enough to allow it to enter and turn in locks with different ward arrangements
spool pin: A pin that has a groove cut around it's periphery. The groove is intended to catch at the shear line as a deterrent to picking.
tip: The very end of part of the key that you stick into the lock first.
toe (of a shackle): That part of the shackle which may be removed from the padlock body.
top master key: The highest level masterkey that fits all the locks in a multi-level masterkeyed system.
top pin: Common name for a "driver pin". This is the pin in a pin stack that sits closest to the spring.
tubular key cylinder: A cylinder whose tumblers are arranged in a circle and which is operated by a tubular key.
tubular lockset: A bored lockset whose latch or bolt locking mechanism is contained in the component installed into the edge bore.
UL listed: Listed in a directory as having passed specific Underwriters Laboratories testing.
wafer: A wafer is akin to a pin in a pin tumbler lock. They are found in wafer locks, which are the kind of locks you'll find on filing cabinets, desk drawers, display cases, cheap fire safes, and car locks. They work differently from pin tumbler locks in that a given wafer is moved in one direction by a spring on its side, and will protrude through either the top or bottom of the sheer line unless it is aligned properly with the key. Because of this, the locks can be made double-sided so a key can be inserted either way, and every other wafer springs in the opposite direction. (thanks Raccoon)
ward: Protrusions that stick out of the sides of the keyway to restrict entry to the correct type of key blank.
