The Olympus OM20 is a 1983 aperture-priority 35mm SLR, sold as the OM-G in North America. It sat between the budget OM10 and the enthusiast OM-2 in the compact OM System line, adding the proper manual mode that the OM10 needed a plug-in adapter to provide.
Specs include the Olympus OM bayonet, an electronically timed cloth focal-plane shutter from 1s to 1/1000s with flash sync at 1/60s, centre-weighted TTL metering, aperture-priority and full manual exposure, a self-timer and an LED readout in the finder, powered by two SR44 cells.
OM20 bodies are plentiful and cheap in the UK, usually well under £100 body-only and often bundled with a Zuiko 50mm f/1.8. It was a popular student camera, so supply is steady; black examples and boxed kits fetch a modest premium over the common chrome bodies.
Check the shutter fires at all speeds on fresh SR44 batteries; the OM20 is electronic, and dead electronics are rarely economic to repair. Foam light seals almost always need replacing on these, so budget for a reseal, and confirm the meter tracks changing light sensibly.