Hitscan
A weapon whose shot lands instantly along a straight line the same frame the trigger is pulled, with no projectile travelling through the world.
Instead of spawning a physical projectile, the engine fires a ray (a raycast) from the muzzle and asks what it first crosses — a hitbox, a wall, nothing. Doom (1993) did this with its shotguns: no bullet was modelled, just a line test against the level. Cheap, exact, and with no travel time.
The opposite is a real projectile with speed and drop, which a player can dodge. The choice is as much design as tech — hitscan rewards aim and snap reactions, projectiles reward leading your target. Many modern games mix the two: hitscan up close, modelled bullets for sniper rifles. The technique leans on the same line-of-sight test AI uses to spot the player.