The term 'KNIGHT's Neighbor' refers to the pieces that are adjacent to a KNIGHT on a chessboard. These pieces include the ROOK, which is represented by the letter 'R' and has four letters; the CASTLE, which is represented by the letter 'C' and has six letters; the BISHOP, which is represented by the letter 'B' and has six letters; and the PAWN, which is represented by the letter 'P' and has four letters. In chess, the KNIGHT is the only piece that can jump over other pieces, so its neighbors are the pieces that are closest to it.