Glitching is a term usually referred to if a user does something that was not the original intention of the developer or takes advantage of a bug within the game to abuse it so that their score, stats or points output increases.

This could be such stuff like getting out of the map in a unwanted way, abusing AI behavior, anything that is not intended in a fair-play environment

If they do this glitches you cannot shoot or see them and they can see or shoot you.