short for 'automatic' (automatic transmission); an informal term referring to a vehicle's automatic gearbox.
彼はオートマしか運転できない。
He can only drive automatic cars.
中古車を買うならオートマの方が楽だと思う。
If you're buying a used car, I think an automatic is easier.
このエリアではオートマの需要が高い。
Automatics are in high demand in this area.