resonance hybrid

A localized valence bond representation of a molecule. This describes pictorially an electronic wavefunction that makes some contribution to the state wavefunction of the system. Resonance hybrids are needed to describe the state of a system when that system is not adequately described by a single Lewis structure.
PAC, 1999, 71, 1919 (Glossary of terms used in theoretical organic chemistry) on page 1961