Dictionary Definition: 

“Any organic compound whose molecule contains one or more hydroxyl groups attached to a carbon atom.”

Selected from OxfordDictionaries.com

Functional Definition:

Alcohols are defined by the functional group OH attached to a carbon chain or alkyl group. The hydroxyl OH group is characterized by hydration and dehydration reactions in which the OH is removed or added. In a dehydration the OH is removed and a molecule of water is formed. In hydration OH is added via a molecule of water.

To name alcohols you add -ol to the end of the IUPAC name after first identifying and numbering your alkyl groups or other functional groups. In the case of ringed structures with alcohol groups are usually called phenols.