S number may refer to: Meter Point Administration Number, often referred to as Supply Number or S-Number, a 21-digit number used in Great Britain to uniquely identify electricity supply points; S number (wool), an international scale measuring the fineness of the threads in woven wool. Singular value, in mathematics, the square root of an eigenvalue of a nonnegative self-adjoint operator. Numbering of compositions by Franz Liszt according to Humphrey Searle's catalogue