Bas relief – from the French basse-relief, meaning low relief – describes a style of sculpture in which design elements project only slightly above the surrounding flat surface, or field. Virtually all standard struck coins are executed in bas relief: the portrait, lettering, and devices rise above the field, but the projection is modest.
Bas relief is the practical standard for circulation coinage because it allows a clean strike in a single blow, resists wear well, and allows coins to be stacked without damage. Most circulating coins throughout history have been executed in bas relief for precisely these reasons.
The term becomes meaningful primarily through contrast with high relief – a more dramatic mode in which design elements project substantially above the field, creating pronounced shadows and a strongly three-dimensional appearance. High relief coins require extra striking pressure or multiple blows, cannot easily be stacked, and are considerably more expensive to produce. They are issued almost exclusively as collector pieces.