A bishop endgame is a phase of the game in which both sides have only bishops (and possibly pawns) remaining on the board.
It is one of the most common endgames in practice, and it falls into two distinct categories: same-colored bishop endgames, where both bishops operate on the same color of squares, and opposite-colored bishop endgames, where each player’s bishop travels on a different color. This distinction is crucial, as it largely determines the nature of the position. Opposite-colored bishop endgames are well known for their strong drawing tendencies — even being a pawn or two down may not be enough to lose, because the attacking bishop can never directly obstruct the opponent’s pawns.
For players rated 800–1400, the first question to ask when entering a bishop endgame is: are my pawns placed on the same color squares as my bishop, or on the opposite color? A bishop whose pawns sit on the same color squares is called a "bad bishop" — its mobility is severely restricted. Placing your pawns on the opposite color to your own bishop frees it up completely, and this is one of the core principles of bishop endgames.