Illustrated Glossary of Organic Chemistry

Diaxial interaction (1,3-diaxial interaction): An interaction (usually repulsive) between two axial substituents on a cyclohexane ring.

On the top face of this chair cyclohexane, the axial methyl groups and axial hydrogen atom experience diaxial repulsion (indicated with the red dashed line). The three axial chlorine atoms on the bottom face also experience diaxial repulsion. The bromine atom does not experience any diaxial interactions in this conformation, because it is equatorial.