A "runway incursion" is a very broad term that includes everything from this accident to a single engine Cessna moving past the hold short line prematurely at a quiet airport.

FAA defines it as "Any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle or person on the protected area of a surface designated for the landing and take off of aircraft." [0]

Many runway incursions run no risk of any accident, but are still flagged as issues, investigated, and punished if appropriate.

[0] https://www.faa.gov/airports/runway_safety/resources/runway_...