If you're an adult when your mother remarries, is her new husband your stepfather (even though he had no hand in raising you)?

Yes, I believe so.

My father remarried when I was in college. I refer to her either as “my stepmother” or “my father’s wife”. I think she prefers the latter, since “stepmother” has a negative connotation (from Cinderella).

yes at least mine is

In the legal sense of the word, yes.

Yes, it’s still more of a legal term than a term of affection.