In mathematics, a quadruple or quadruplet is an n-tuple with n being 4. This means it depicts four element, with the order of the elements carrying meaning. This differs from a set, where the order of the elements is meaningless and where no element could exist more than once. Derived from this abstract meaning, it is used in several other contexts including: · In football, a quadruple is the act of winning four trophies in one season. · To quadruple a magnitude is to multiply it by 4. · Quadruplets are four children born in one pregnancy. See Multiple birth. · A quadruplet is a type of note in music (see tuplet). · A redundant backup system that has three secondary systems to take over if the primary fails. · A figure skating jump with four revolutions. Sequences and series