Complex sentence: In digital photography, medium format refers to the use of cameras adapted from medium format film gear, fitted with digital backs incorporating sensors larger than 24 by 36mm (the typical frame size used on 35mm film).
Split into simpler sentences: In digital photography, medium format refers to the use of cameras morified or adapted from medium format photography on film. Often, medium format film cameras can be fitted with digital backs, incorporating sensors larger than 24 by 36mm (the typical frame size used on 35mm film).