Bughouse is chess on two boards. You and your partner sit at different boards and play opposite colours.
Every piece you capture is handed to your partner, who can drop it on any empty square on their board instead of making a move.
Pawns can't be dropped on the back ranks · a promoted piece comes back as a pawn · dropping into checkmate is allowed, and it's how most games end · you may sit and burn your own clock while you wait for a piece.
One board finishing ends both — it's a team result.
Capture a piece → your partner can drop it. You always play the opposite colour to your partner. Pawns drop on ranks 2–7, drop-mate is allowed, promoted pieces come back as pawns.