I'm splitting hairs here but the definition of runway incursion I'm used to:
"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."
In Tenerife both aircraft were correctly authorised to be on the runway at the time. The accident occurred when the Captain of the KLM flight decided they would take off even though they didn't have a clearance while PanAm was still trying to find the exit in the fog.
A horrible accident indeed but not by this definition, a runway incursion.
Wikipedia