Illustrated Glossary of Organic Chemistry

Condensation reaction: A reaction in which two or more molecules combine to form a larger molecule, with the simultaneous loss of a small molecule such as water or methanol. While this occurs in many reactions, the term is usually reserved for reactions in which a new carbon-carbon bond is formed.

In this aldol condensation reaction one molecule of acetone and one molecule of benzaldehyde are combined with simultaneous loss of a water molecule.