Just about everyone reading this is probably familiar with these three key facts about C:
The C standard doesn't have a single word for this. It uses the word "conversion" when defining behavior (1) in 6.3.2.1p3, "equivalent" when defining behavior (2) in 6.5.2.1p2, and "adjustment" when defining behavior (3) in 6.7.6.3p7.
I am old-fashioned, and don't think there's anything wrong with calling this "array/pointer equivalence", provided it is clear in context that you are talking about expressions where (1) happens or function declarations where (3) happens. However, a more palatable term for the people who don't like "equivalence" would perhaps be "array-to-pointer conversion", since this confuses people most often when it's (1), I think.