Sigma Bond Chemistry Definition

This shows the electron distribution in a sigma bond between two neighboring atoms.
This shows the electron distribution in a sigma bond between two neighboring atoms. Todd Helmenstine

Sigma bonds are covalent bonds formed by direct overlapping between two adjacent atom's outermost orbitals. The single electrons from each atom's orbital combine to form an electron pair creating the sigma bond.

Sigma bonds are generally denoted by the Greek letter σ.