Illustrated Glossary of Organic Chemistry

Anti: Atoms, groups, or other portions of a molecule that point in opposite directions. These entities have a dihedral angle of more than 90o.

The two methyl groups are anti and staggered in the anti-periplanar conformation of butane.
Verify the CH3/CH3 dihedral angle of 180o with a molecular model.

The electrophilic addition of Br2 to an alkene is an anti addition.