Baseball is a game played between two teams of nine players each. The game is divided into nine innings, each divided into two halves. In the top half of the inning, the players of one team successively come to bat and attempt to score runs, while the other team plays in the field and attempts to stop the offensive team from scoring. In the bottom half, the teams swap places. The team with more runs at the end of nine innings is the winner of the game. The bases are the four points of the baseball diamond (first through third bases and home plate) that must be touched by a runner in order to score a run.

Source: PBS