One of two stereoisomers that differ in configuration at one chiral center.

One of two steroisomers with more than one chiral center that differ in stereochemical configuration at only one.

In chemistry, an epimer is a stereoisomer of another compound that has a different configuration at only one of several chiral carbon centers. Stereoisomers include enantiomers and diastereomers, both which contain a chiral carbon center (excluding geometric isomers, which is a class of diastereomers).