Illustrated Glossary of Organic Chemistry

Vicinal (vic): Describes two atoms or groups bonded to adjacent carbons. The prefix vic may be added to the molecule's name to indicate the vicinal relationship.

A vicinal diol (a glycol).   
A geminal diol.

In a vicinal diol, the two OH groups are on adjacent carbons. In
a geminal diol, the two OH groups are bonded to the same carbon.
Addition of Br2 to an alkene
produces a vicinal dibromide.