Academic division of verification approaches

Hi all,

I am writting my Master thesis and I need to make sure of some academic definitions in verefication field. Is this true to divide verification approaches like this?
1-functional verification
2-physical verification
3-formal verification

As I have read some articles some people define formal verification as a subset of functional verification, but there are some techniques in formal verification (like equivalence checking) which are just comparison of 2 different design representation.

I appreciate any guide on this and is there any other major approach that I have accidently missed in this division? any resource to look this up is very much appreciated.

Thank you in advance!