Both terms are used to express an expiation or ransom (based on the actual context).
See for example (2:85), (2:184) (in context of fast), (2:196) (in context of hajj), (2:229), (3:91), (5:36), (13:18), (37:17), (47:4), (57:15) and (7:11) where the qur'an quotes the term الفدية fidyah (in cases meaning both).
My question is what is the distinction between both Terms?