To me, a meme is something that everybody posts in their journals and whatnot that just gets around. That includes surveys, quizzes, and all sorts of random things. Basically, it's an internet fad that makes its rounds on the internet.

In the case of love (or hate) memes, it's a post or comm that people post in anonymously to express their love (or hate) for certain subjects/fandoms/people etc. In a way, fandom secrets is a meme.

I feel like I didn't explain that well enough. A meme is so many different things.... Um, here's further references: wikipedia: internet meme (http://en.wikipedia.org/wiki/Internet_meme), urban dictionary: meme (http://www.urbandictionary.com/define.php?term=meme)