I don't know what PHP stands for either, but BB stood for Bulletin Board. PHP is the programming language it was written in. You could have just said forums and been more accurate; most people know what those are.

But no, Lemmy is not like a forum, it's like a more liberal Reddit, which was like Digg but more expansive, and Digg, in turn, was like a better Fark (though, some will fight you for saying that). All of those are news aggregators. Forums work differently.

Forums are still around, but they aren't as popular as they once were.

Also, "won't" and "can't" do not mean the same thing. "Can't" is kind of a funny concept when it comes to knowledge on the Internet. For example, a DuckDuckGo search quickly reveals that PHP used to stand for "Personal Home Page" but now stands for "PHP Hypertext Preprocessor." But never mind that, it's a scripting/programming language for websites and forums and things like that.