In short
The legal priority for one road user over another at intersections, merges, and pedestrian crossings.
Right of way is the legal priority for one road user over another. Specific rules vary by state but common patterns: yield to pedestrians at all crosswalks, yield to traffic already in a roundabout, yield to vehicles on the dominant road at a non-signaled intersection.
Failing to yield right of way is a common road-test fault.