Illustrated Glossary of Organic Chemistry

Antibonding molecular orbital: A molecular orbital formed by out-of-phase overlap of atomic orbitals. It is higher in energy than the atomic orbitals from which it is formed. Antibonding orbitals are designated with * (i.e., σ* or π*).

Out-of-phase overlap of s orbitals forms a the antibonding component of a σ bond (a σ* orbital).

Out-of-phase overlap of p orbitals forms the antibonding component of a π bond (a π* orbital).