A fish in poker is a bad player who doesn’t know much about the game strategy and is very likely to lose in any given session unless they gets lucky.
It is somewhat of a derogatory term so no one likes to be called a fish.
There is not one strict definition of a poker fish. In general, this type of player makes fundamental strategy mistakes, whether they hero call too much with weak hands, bluff way too often, or barrel in too many pots – or a combination of these things.
Players love having a fish at their table as a villain, but because of the nature of the game, even these players win sometimes. When this happens, the best course of action is to stay silent and not berate the winning player, as this may cause them to leave. Upsetting a player who’s perceived to be a fish or a whale is referred to as “tapping the glass.”
