What exactly is "slut shaming", and why is it so wrong??

Interesting that I have a 20 something son who has zero problems with the young women his age. Many healthy relationships with women including best friends and romantic interest(s). He goes to a liberal school, he’s actively involved in leadership on campus and, in such a role, has had to deal with instances/problems on campus that classmates have had. He has more problems with the attitudes/behavior of some young men his age. I’ve heard NO issues whatsoever from him with the behavior of young women his age. Zero. Zilch. To hear that your boys are bothered enough to be wary of women in their 20s, @momofthreeboys, sounds really odd to me. But, having been raised in a family of independently minded women, maybe my kid is used to it. Both my son and husband are pretty ardent feminists themselves.