A hitscan in computer games, most commonly in first-person shooters, is where the programming system determines where the gun/object is pointing, casts out a ray in that direction when shot, for a certain range programmed into the system, and see if that ray comes in contact with any object in the line of fire.
Source: https://en.m.wikipedia.org/wiki/Hitscan#:~:text=A%20hitscan%20in%20computer%20games,in%20the%20line%20of%20fire.