I can't find any ICAO document that defines a Taxiway Incursion, but I can find some online presentations which were presented at ICAO workshops or seminars that loosely refer to Runway/Taxiway Incursions! Runway Incursion is well defined and there is no doubt about its meaning or significance, but the question is: is every wrong turn during taxiing considered a taxiway incursion? If so, according to what official definition?
I haven't seen it explicitly defined, but the meaning can be inferred by comparison to the definition of a runway incursion. ICAO defines a runway incursion 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." Thus a taxiway incursion would be "any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle or person on a taxiway.
There doesn't need to be an official definition to use it in a presentation. If you say "Runway/Taxiway incursion," everyone who knows what a runway incursion is can pretty much guess what you mean by a taxiway incursion.
A wrong turn while taxiing is only a runway incursion if it takes you across the hold short line for a runway. Presumably it's a taxiway incursion if it takes you onto a taxiway that you are not supposed to be on.