The Hasselblad 500EL/M is the 1971 motor-driven variant of the classic 500C/M, a 6x6 medium format film SLR in the V System. It replaced the 500EL, adding the interchangeable focusing screens photographers had asked for; NASA famously flew EL-series bodies on the Apollo missions.
It takes Hasselblad V-mount Carl Zeiss leaf-shutter lenses and A12/A24 film magazines, exposes 6x6cm frames on 120 or 220 roll film, and its built-in motor winds on automatically after each frame at roughly one frame per second, powered by rechargeable cells in the base.
EL/M bodies sell well under a manual 500C/M in the UK, often £300-600 body-only, because the motor adds weight and battery uncertainty. That makes them one of the cheapest routes into the V System, and studio-kept examples tend to be lightly worn.
Original NiCd packs are usually dead; check whether a 9V battery adapter is included, as listings with one are worth paying more for. Test that the motor cycles smoothly, check any included magazine for light seal wear, and remember body-only prices still need a lens and back.