In poker, the term fish describes a bad player that doesn’t have much knowledge about the game and is unlikely to win on any given day unless they get lucky.
Like many other poker terms, the expression “fish” doesn’t have any strict definitions. It is simply a player that other players playing in the same games see as someone who they can easily beat.
For example, you could hear someone say: “Yeah, I know Jim. He’s the biggest fish in our home game – he drops a few buy-ins every time we play, and I don’t think I’ve ever seen him win.”
Generally speaking, you want to play games with plenty of fish, and you never want to be the fish. Also, keep in mind that bad players can get better, so just because someone was a fish when you played them two years ago, it doesn’t mean that they haven’t improved in the meantime.