For me, it has one simple basic meaning, and that is..... to blog about books and get a conversation going with other like minded bookish fans.
But if you would like me to elaborate:
It means being able to let lose with your love (or hate) of a book and or author... and not feel like everyone is looking at you weird. Well, at least not TOO weird.
It means reading the same book with other bloggers and talking about it (aka a read along.)
It means challenging each other to "read more books!" Or to branch out and try something new. Or to remember and revisit the "good old books" or to participate in something bookishly fun.
It means commenting as much as you can on other blogs to help facilitate the conversation mentioned above.... which then leads to connections and relationships with other bloggers.
It means writing posts that get people thinking about and talking about books....whether that's reviews, lists, discussions, etc.
It means supporting the general bookish community, both online and off, and supporting authors by putting your money where you mouth is... if you at all can.
And finally, it means having fun!