Epimers are sugars that differ in the configuration of just one specific carbon atom (other than the anomeric carbon) while being identical in the rest of their structure.
Example 1. Glucose and Galactose are C4 epimers (means that they differ in the configuration around the 4th carbon atom)
Example 2. Glucose and Mannose are C2 epimers (means that they differ in the configuration around the 2nd carbon atom)
