In my view, friendship is the relationship of friends.<img alt="" src="http://www.italki.com/fckeditor/editor/images/smiley/msn/tounge_smile.gif" />. There are many levels of friendship such as : not so close, normal, close...friends. The fewer friends, the deeper relationship.

It's reallly hard to define friendship these days since people have different intentions. And we don't actually see those hidden intentions within them. There are people who befriend us for numerous reasons, and it is rare these days to know that, they befriend us for friendship.

When I was younger I thought my friends are the people who I can have fun or party with... 
but then we parted, we're studying and living in different cities, a lot of these 'party friends' left but some of them stayed and our friendship is stronger. So for me friendship is trust and staying by each others side all the time  . 

Currently it's a very confusing term that confuses me a lot. I would call what you call "bff" somewhat my mentors, and I'm going through a period of my own, of anti-facebooklised-friendism.