Three-Center, Two Electron Bonds Definition:

A bond in which two electrons are associated with three atoms, such as in diborane (B2H6).

Three-Center, Two Electron Bonds Explained:

Molecules that have lower than two valence electrons per bond are said to be electron deficient. The bonding in a molecule is interpreted in terms of a symmetric three-center (3c) bonding molecular orbital containing the two valence electrons.