Definition of shot
Taking a shot is the act of moving up a limit to try your luck. If you are an NL100 player and you see several bad players at an NL400 table, you might think you are going to take a shot to try to make a money shot. When you take a shot, you have to be rational and not emotional.
Good and bad reasons to take a shot
Good reasons to take a shot are that you are a big winner on the lower limit and you want to test the waters on the higher limit. Another reason to take a shot is to bumhunt, i.e. because you have seen several very weak players at a higher limit. Bad reasons to take a shot are because we are completely tilted and want to rebuild at a higher limit (chasing losses) or because we are bored with the limit we are playing at and are looking for more excitement.