noun: (mathematics) The determinant of a skew-symmetric matrix, capable of being written as the square of a polynomial in the matrix entries.
noun: (historical) A member of a circle of artists that met at Pfaff's, a restaurant on Broadway.
noun: Alternative letter-case form of Pfaffian [(mathematics) The determinant of a skew-symmetric matrix, capable of being written as the square of a polynomial in the matrix entries.]