Calf
The belly or fleshy hind part of the leg below the knee.
The calf is made up mainly of the gastrocnemius muscle (which comes from the Greek 'gastroknemia' meaning calf of the leg, from 'gaster' (gastr-), belly, + 'kneme,' leg).
The word 'calf' comes through the Anglo-Saxon, it is thought, from the Indo-European 'gelbh' meaning to bunch up, as do the muscles of the calf.