The term 'PREFIX FOR SKELETON' can be answered with two words: ENDO and EXO. ENDO is a four-letter prefix meaning 'WITHIN' or 'INNER, ' while EXO is a three-letter prefix meaning 'OUTSIDE' or 'OUTER.' These terms are often used in biology to describe the location of organs or other body parts relative to the skeleton. For example, an endoskeleton is an internal skeleton, while an exoskeleton is an external skeleton.