Often shortened to regen, the ability of a drive to return current to the mains supply for example when braking a motor.
Found on http://www.encyclo.co.uk/local/20823
Re·gen'er·a·tive adjective Of or pertaining to regeneration; tending to regenerate; as, regenerative influences. H. Bushnell. Regenerative furnace (Metal.) , a furnace having a regenerator in which gas used for fuel, and air for supporting combustion, are heated; a ... Found on http://www.encyclo.co.uk/webster/R/39