A Technic supercar is a car which has all the features of a real car which can be practically reproduced with Technic.
The minimum features are:
Working steering
Working engine
Suspension on all wheels (not necessarily independent suspension)
Transmission
Cars do not necessarily have to be "Super Cars", such as Lamborghinis, Ferraris, etc.
Not to be confused with the group "Technic Super Cars" which is only for sports cars.