A region of relatively high electron density between nuclei which arises at least partly from sharing of electrons and gives rise to an attractive force and characteristic internuclear distance.
See also: agostic, coordination, hydrogen bond, multi-centre bond
Source:
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1101 (https://doi.org/10.1351/pac199466051077)