An aimhack or aimbot is an cheat/hack that auto aim for you.
By using this cheat or hack you will have a 100% hit rate.
You will not only have a 100% hit rate, it also will be headshots only as that is
the fastest way to kill a enemy player.
You should keep in mind that the more advanced aimhack(bot) have settings that this
will not be 100% accurate to avoid suspicious behavior and thus try to avoid being caught.
An aimhack or aimbot are most likely with an autoshoot option for fast triggering.
Example: