Definition of shot
Taking a shot is the fact of going up the limit to try your luck. If you're an NL100 player and you see several bad players at an NL400 table, you might think that you're 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 limit below and want to feel the ground on the limit above. Another reason to take a shot for bumhunter is that you've seen many very weak players at a higher limit. Bad reasons to take a shot are because you're completely tilted and want to get back to a higher limit (chasing losses) or because you're jaded about the limit you're playing at and are looking for more excitement.