Source : Webster's Revised Unabridged Dictionary (1913)

Tergum \Ter"gum\, n.; pl. {Terga}. [L., the back.] (Zo["o]l.)
   (a) The back of an animal.
   (b) The dorsal piece of a somite of an articulate animal.
   (c) One of the dorsal plates of the operculum of a cirriped.