CHEM 121 glossary
Resonance hybrid
The real structure of a species with resonance: a single, unchanging average of all its resonance forms, weighted toward the forms with the best formal charges. It does not flip between the forms.
Benzene is drawn as one form, but the real molecule is the hybrid of two.
Example
In benzene every C–C bond is 139 pm, between a C–C single bond (154 pm) and a C=C double bond (134 pm), with bond order 1.5.