Term used by some authorities to refer to stereoisomerism resulting from the arrangement of out-of-plane groups with respect to a plane (chirality plane). It is exemplified by the atropisomerism of (E)-cyclooctene (chiral plane = double bond and attached atoms) or monosubstituted paracyclophane (chiral plane = substituted ring). The configuration of molecular entities possessing planar chirality is specified by the stereodescriptors \(R_{\rm{p}}\) and \(S_{\rm{p}}\) (or \(P\) and \(M\)).