Multicentre bonding describes a bonding interaction distributed over more than two atomic centers. A two-center localized electron-pair picture may then fail to represent how the occupied molecular orbitals stabilize the structure.
A standard example is a bridging hydrogen in diborane, where a three-centre two-electron bond extends across a boron-hydrogen-boron unit. The electron pair belongs to the whole three-center interaction, rather than to two independent ordinary bonds. This helps explain electron-deficient molecules without requiring each apparent atom-to-atom connection to contain its own pair of electrons.
New to topics? Read the docs here!