Redundant organ
A redundant organ was any organ which presented in numbers beyond that which was strictly necessary for survival.

In 2152, Gosis described Jonathan Archer and Malcolm Reed's second kidneys as  "redundant renal organ"s. ()

Klingons had an abundance of redundant organs, a concept they referred to as brak'lul: a redundancy that evolved because it allowed the Klingon warriors to survive otherwise crippling damage. (, , et al.)

See also
 Vestigial organ
Organs