Epimers

Epimers are carbohydrates which vary in one position for the placement of the -OH group.  The best examples are for D-glucose and D-galactose.  Both monosaccharides are D-sugars, meaning that the -OH group on carbon-5 of these hexoses is located on the right in Fischer Projection. The only difference between D-glucose and D-galactose is on carbon-4. For D-glucose, the -OH is on the right in Fischer Projection, and for D-galactose, the -OH group is on the left.  That single different makes D-glucose and D-galactose epimers. They are not enantiomers, or diastereomers, or isomers, they are only epimers.