A symmetry in many models of supersymmetry, in which the ordinary particles have an R-parity of +1 and their supersymmetric partners have an R-parity of −1. If R-parity is a valid symmetry, then the supersymmetric particle with the lowest mass, known as the lightest superpartner (LSP), is a stable particle that may be an essential ingredient of dark matter. Models have been considered in which R-parity is a broken symmetry.