I'll try a non-sarcastic stab at this... the ones I'm not competent to explain I've left blank, and I fully expect some folks will want to pick nits about some of my definitions.
Oh, and Jammer? Your advice about liking what you like is not bad, but it's hardly useful for someone who's trying to get an idea of what the trigger might be like on a gun he's never fired but his friend has.
0) adjustable trigger -- a trigger that is "easily" adjusted by the user to have a different pull weight. (See #s 5 & 6)
1) backlash
2) break -- the point at which the trigger allows the hammer to fall, accompanied by a sudden release of tension. The ideal break is sudden and definite.
3) creep -- a trigger is said to creep when it does not have a consistent, clean break. Once the trigger reaches the break point, it should not be possible to move it further to the rear, even slightly or slowly, without a crisp break.
4) crisp -- sudden and definite, with no extra movement possible.
5) engagement
5a) hair trigger -- a trigger that breaks from an extremely light touch. Trigger pull weight is measured by the number of pounds of pressure required to pull the trigger past the break. A "hair trigger" is a trigger that could be pulled past the break by the weight of a single strand of human hair. Obviously a descriptive term that is never strictly accurate, it is often used in news stories to denote a trigger that can easily be pulled by a normal human being instead of by someone with the hand strength of an upland gorilla.
6) heavy -- a trigger that requires a lot of pressure to be pulled past the break. "Heavy" is subjective and depends upon the gun type, but generally speaking, in a handgun anything under 4 pounds is light, and anything over 6 or 8 pounds is heavy. Rifles usually have much lighter triggers than handguns, and thus "heavy" on a rifle might be "light" on a handgun.
7) length of pull / pull length -- the distance the trigger must travel in order to fire a shot.
8) lock time
9) long -- a trigger with an exceptional length of pull. Like "heavy" and "light," "long" is a subjective term which depends upon the type of gun.
10) over-travel -- after the break, the trigger should stop completely. If it does not, that's over-travel, so called because the trigger keeps "traveling" after its journey is completed.
11) pre-travel -- Some triggers can be pulled slightly backwards before you can feel any tension and before any other movement is initiated within the gun -- thus, this is travel that begins before the trigger is doing any work at all.
12) pull -- see #s 5, 6, & 7. Pull describes the entire sensation of making the trigger complete its journey past the break.
12a) reset -- The point of the trigger's return journey at which the gun's internal mechanisms are ready to fire another round. On many guns, after the shot has fired, if you hold the trigger to the rear and then slowly release it, you can feel or sometimes hear an audible 'click' as the trigger reaches the reset point. (Doing this every time while re-aligning the sights is called "follow through," and it helps to improve accuracy. The next shot is then fired from the reset point, rather than allowing the trigger to complete its return toward the front.) The reset point varies greatly from one type of gun to another, and some guns do not reset until the trigger has been allowed to complete its entire return journey.
13) rough -- a gritty or inconsistent feel to the trigger pull.
14) sear break
15) short -- the opposite of long. A trigger that doesn't have to travel very far before the break.
16) slack -- see #11.
17) takeup -- see #s 11 & 16
18) trigger slap -- flapping your finger onto the trigger and yanking it to the rear, usually accompanied by flapping your finger immediately back off the trigger at the moment the shot fires. A bad thing, because it invariably misaligns the sights and sends your shot wild.
19) trigger stop
pax
With a knowledge of the name comes a distincter recognition and knowledge of the thing. -- Henry David Thoreau
