The configuration of a molecule is the permanent geometry that results from the spatial arrangement of its bonds. The ability of the same set of atoms to form two or more molecules with different configurations is stereoisomerism. Used as drugs, compounds with different configuration normally have different physiological activity, including the desired pharmacological effect, the toxicology and the metabolism.
Configuration is distinct from chemical conformation, a shape attainable by bond rotations.
References
Molecular configuration Wikipedia(Text) CC BY-SA