Pool Rummy is a multiplayer card game that can be played with 2 to 6 players. There are three main formats: 101 Points, 201 Points, and Best of 3. In 101 and 201 Points formats, players accumulate points until they reach 101 or 201 points respectively and are eliminated. In Best of 3, players compete over three rounds and the player with the lowest total points after three rounds wins. The game has specific rules around valid card combinations, scoring points for dropping out early, and determining a winner.