Illustrated Glossary of Organic Chemistry

Gauche: The relationship between two atoms or groups whose dihedral angle is more than 0o (i.e., eclipsed) but less than 120o (i.e., the next eclipsed conformation). A conformation which has one or more gauche interactions is can be called a gauche conformation.

The anti-staggered conformation of butane has six gauche relationships.

This is a gauche conformation because the methyl groups are gauche.
This conformation has a total of six gauche relationships.