Assault weapon is a buzz word like pit bull TYPE, it is not an actual technical term in the firearms community.
Actual technical terms
Bolt: a firearm part which holds a round of ammunition in the chamber of the barrel poor to and during firing and generally contains a firing pin
Cylinder: firearm part that holds multiple chambers separate from the barrel and rotates those chambers in line with the barrel
Chamber: the portion, usually attached, of the barrel that is shaped like the round of ammunition and contains the pressure during firing
Firing pin: a small pin that strikes the primer on a round of ammunition causing it to fire, usually contained within the bolt or on the hammer of a firearm
Hammer: part of a firearm held under spring tension, when that tension is released the hammer moves rapidly forward striking either the round of ammunition or the rear of the firing pin causing the round to fire
Automatic/full automatic/full auto: multiple rounds are fired when the trigger is pulled
Semi automatic/semi auto/ self loading: pull the trigger and a single round is fired but the weapon cycles itself and prepares to fire the next round w/o any action on the part of the shooter
Pistol: all encompassing term for handguns, can be single shot, multibarrel, revolver, semi auto or full auto
Revolver: a pistol w/ a revolving cylinder containing multiple chambers containing the cartridges to be fired
Double action: two actions are performed by the weapon when the trigger is pulled. on a striker fired pistol the striker/firing pin is put under spring tension and then released causing the cartridge to fire. On a hammer fired pistol, the hammer is cocked & then released causing the cartridge to fire. Term is descriptive of both revolvers & semiautomatic pistols, but applies to rifles ONLY if the rifle is a revolving cylinder rifle like the Rossi Judge. Because of the heavy, long & irregular trigger pull double action is generally less accurate. Most double action semi auto pistols are single action after the first round is fired.
Single action: means a single action is performed by the weapon upon pulling the trigger, specifically the firing of the weapon. Descriptive use of the term is the same as double action. Most double action hammer fired weapons can be fired single action if the shooter manually cocks the hammer. Because of the lighter, shorter & crisp trigger pull, single action is generally more accurate shooting.
Pump action/slide action: a type of fire arm, generally a rifle or shotgun, that requires the shooter to manually eject a fired case, cock the hammer or put the firing pin under spring tension, transfer an unfired round of ammunition from a magazine to the chamber in preparation of being fired. The shooter does this by means of a slide or pump that is moved backward then forward parallel to the linear axis of the barrel, usually around the outside of the magazine. Most pump actions are striker fired. Examples include Remington 7600 rifle, colt lightning, and Ithaca model 37
Lever action: same as the pump action except the shooter performs the mechanical functions by means of a lever moved forward then backward in an arc. The lever is moved in an approximately 90 degree arc that begins with the lever parallel to the linear axis of the barrel and ends perpendicular to the linear axis and then returns to the perpendicular starting position. Most lever actions are hammer fired. Examples include Winchester models 1866, 1873, 1887 shotgun, 1895 & Marlin models 1894, 1895 & 336
Bolt action: again the shooter manually operates the functions of the weapon. In this case by pulling backward on a handle attached directly to the bolt of the weapon and then pushing forward on the handle. Depending on the exact design, the shooter will often be required too use the handle to rotate the bolt 60-90 degrees before backward movement & after forward movement. Examples are the SMLE, K98 & 1903A3 Springfield.
Machine gun: a fully automatic weapon chambering a high powered round, fed by a belt of ammunition whose purpose on the battlefield is to provide extended bursts of automatic fire usually to suppress the movement of opposing personnel so that friendly personnel may move to positions which allow them to make individual killing shots. Also used to destroy hostile equipment and vehicles. Examples are the RPD, PKM, M2, and M60
Submachine gun: a fully automatic firearm chambering a pistol caliber round, intended to fire a large number of smaller less efficient bullets at short range, preferably in an urban combat environment. Effective range is generally less than 200M. Examples are the Uzi, MP5, Thompson 1927 & the M3 "grease gun"
Battle rifle: any full powered rifle built for the harsh conditions of combat generally semiautomatic or bolt action. Can effectively be used to kill people beyond 1000M. Examples are the M1 Garand, K98, SMLE and the 1903A3 Springfield
Assault rifle: a selective fire (full or semi auto) rifle, chambering a midpowered round intended to fall in between the capabilities of a full powered battle rifle and the less effective sub machine gun. Chamberings are either weak medium bore rifle rounds like the 8mm Kurtz or the 7.62x39mm soviet round or high velocity small bore rounds like the 5.56X45mm NATO or the 5.45x39mm soviet rounds (both are 22s on steroids). Effective range is considered to be between 300-500M. Examples are STG 44 "sturmgewehr", M16, M4, HK 53, AK47 & AK74
Machine pistol: a fully automatic pistol intended to be effectively fired with one hand. Mostly a gimmick or last ditch weapon. More for cops and wannabe spies. Extremely difficult to shoot well beyond kitchen table ranges. Examples include MAC-10, Skorpion vz 61, & the Mauser C96