A2 Tool Steel (carbon steel): A2 is the most common air hardening grade of tool steel currently used.  It contains 1.0% carbon, 5.0% chromium, and 1.0% molybdenum.  It is not a stainless steel.

Abalone: A type of scale or handle material made from Abalone Shell (Haliotidae Haliotis).  Today, most abalone is harvested from commercial abalone farms. There are numerous restriction on the harvesting of wild abalone.

Ad (Advertising) knife:  A small knife, normally a pen or small utility knife that advertises a business, institution, or event.

Aircraft Aluminum:  In the aerospace engineering field aircraft aluminum usually refers to aluminum 7075, an aluminum alloy, with zinc as the primary alloying element. It is strong, with strength comparable to many steels, and has good fatigue strength and average machinability, Its relatively high cost limits its use to applications where cheaper alloys are not suitable. It is sometimes used in knife handles for scales or liners.

Alox: A propriatroy name for the aluminum used by Victorinox. Alox is used primarily for liners in Swiss Army Knives, however it is also used as a scale material for Alox Swisss Army Knives.

Annealing: in metallurgy it is altering the properties of metal at the microstructure level by exposing it to heat in various specific scientific formulas. The purpose is to normally improve the metal’s strength, toughness, hardness, wear, etc. for a specified purpose.

Antique:   
1) Officially an antique knife is a knife that predates mass production (1830) and has historical significance.

2) Unoffically, An often ill-defined and therefore meaningless term used to sell knives; especially online.

Antler:  See Stag

Arkansas Toothpick:
1) a large knife with a prominent cross-guard, a large grip and heavy pommel and large heavy double edged blade, triangular in shape that is very wide at the top and tapering to very sharp point, balanced for throwing 

2) any large fix blade knife 

3) a bowie knife

Armor Piercing Blade: Normally a short, thick tanto style blade desigend to pierce thin steel or armor plating. 

Art knife:  A knife that is more for show than anything else.  They can still be functional but are not really designed for use as a tool or weapon.

Assisted Opening: A knife that uses a spring or other device to assist in the opening of the blade. Unlike switchblades or automatic knives, assisted opening knives require the operator to touch the blade in order for it to open. This is usually done with the aid of a flipper, thumb stud, or thumb hole which is an integral part of the blade. Once the blade begins to open a spring or other device takes overs and finishes blade deployment. Compare to Switchblade and Flipper Knife.

ATS-34: A stainless steel considered superior to 440C Stainless Steel in most aspects but may not be as tough.

AUS-6: Japanese stainless steel, roughly comparable to, if not slightly better than 440A (AUS-6, .65% carbon)

AUS-8: Japanese stainless steel, roughly comparable to, if not slightly better than 440B (AUS-6, .75% carbon)

AUS-10: Japanese stainless steel, roughly comparable to, if not slightly better than 440C (AUS-1.1% carbon)

Austentic Stainless Steel.  Stainless steel with at least 7%  nickel added, making the steel virtually useless for a knife blade.  Austentic stainless steel is normally non magnetic and is sometimes used for knife handles or liners due to its softeness.

Automatic Knife: Technically any knife with a retractable or folding blade that can be opened one handed through the use of release, however, the term is normally reserved for knives commonly refered to as swtch blades (USA) or flick knives (UK)

Auto or Automatic OTF: A spring assisted knife with a retractable blade that deploys point first from the knife's handle when some type of release such as a button ot lever is pressed. The blade must then be manually retracted into the handle by pulling back on the release which follows a channel that is cut into the handle. Also called an Single Action OTF (see Gravity Knife and Double Action OTF for comparison.

Awl:   A pointed blade sometimes with a sharpened edge used for punching holes in leather or wood.  It can also be used to dislodge stones from hooves.