delocalization of a free electron pair (n) into an antibonding σ-orbital (σ*).
See: delocalization, hyperconjugation, resonance
Source:
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1146 (https://doi.org/10.1351/pac199466051077)