Centaurism is a term created by Sigmund Nastrazzuro referring to the phenomenon of evolution repurposing a pair of limbs for something other than locomotion. The name comes from cases such as the praying mantis or mantis shrimp, where posture changes and the repurposed limbs are used for fighting or manipulation. However, the term also applies to cases where the limb takes on other functions, such as sensory or balance; and a change in posture does not always occur.
Crabs' forelimbs developed into grasping hooks and crabs adopted an eight-legged gait. Wings can also be adapted for new purposes, as in the case of flies; their rear pair of wings became a pair of sensors to help enable stable fast flight.
Often, limbs will be freed from the task of locomotion without any apparent new function. For example, kangaroos and Tyrannosaurus adopted a two-legged gait and seldom use the forelegs. Possibly a change in posture was the main driving force in these cases, whereas in centaurism, the change in posture is an effect of adaptation to the limbs' new function.