I have a simple definition of Rigpa:

Rigpa is existential anti-foundationalism.

This can be also called "The nature of states": no state is foundational. No state provides a reference frame or measure of other states.

Rigpa is to existentially recognize the nature of states. That is not, in itself, a state, and is compatible with all possible states.

Ideas about realization or awakening, such as "realizing emptiness" or "awakening to non-duality" often re-introduce a subtle reference state. Insofar as this occurs, "emptiness" and "non-duality" are not Rigpa, though such emptinesses and non-dualities, as with all other states, are compatible with Rigpa.