Piste
A marked, patrolled and usually groomed ski run at a resort, graded by difficulty and maintained for skiing and snowboarding.
Pistes are the backbone of any ski resort. They're prepared daily by snowcats (piste bashers), patrolled by ski patrol and signposted at the top and along their length. A typical resort publishes a piste map that colour-codes each run by difficulty so skiers can choose terrain that matches their ability.
Outside Europe, pistes are more commonly called 'runs' or 'trails'. In either case, skiing inside resort boundaries on marked runs is considered on-piste.