To call is to match a bet or match a raise. A betting round ends when all active players have bet an equal amount. If no opponents call a player's bet or raise, the player wins the pot. The second and subsequent calls of a particular bet amount are sometimes called overcalls.
Each hand has a rank, which is compared against the ranks of other hands participating in the showdown to decide who wins the pot. In high games, like Texas hold 'em and seven-card stud, the highest-ranking hands win. In low games, like razz, the lowest-ranking hands win.