Can someone explain to me what "boy mom" means?

I have a 21 month old son and when I tell people that I have a son, they say "Are you a boy mom?" Or I have a friend who is trying to get pregnant and she always says, "If I have a boy, I won't be a boy mom". I do not understand what people mean when they say "boy mom".

I have a boy, so I guess I am a boy mom. I don't see it as a bad thing? Is there something that I am missing?