The science of grafting mechanical/electronic enhancements on organic creatures, oftentimes by replacing limbs with robotic parts or even mechanical weapons (such as an Arm Cannon), for instance, though often it's only called cybernetics if it's a smidge more complicated. Cybernetics (from Gratuitous Greek for "piloting", because Everything Sounds Futuristic in Greek) is the study and development of regulated systems; a cyborg (short for cybernetic organism)