Bughouse is a variant of chess played by four players in teams (partnerships) of two on two separate chessboards. Each partner plays an opposing team member with the goal being to win the game by normal means (checkmate or timeout).
One partner plays Black, the other White. Partners help each other by capturing enemy pieces which their partner may then place (drop) on an empty square on their turn. Click here for more details and the full rules, and Click here for Tips for Beginners
Rules
When you capture one of your opponent's pieces, it is immediately passed to your teammate's "piece bank" for him or her to use at their discretion.
On any turn, instead of making a move, a player can "drop" any piece from their "bank" to any open square on the board.
Pawns may not be dropped on the 1st or 8th ranks.
A pawn that is placed on the 2nd rank may move two squares on its first move, as in standard chess.
Pawns that have promoted and are then captured go into the "bank" as pawns, not as the piece to which they promoted. Such promoted pieces are called "counterfeits."
A bughouse game is over when a game on either board ends in checkmate, resignation, or timeout.
A bughouse game on chess.com