A meme (pronounced /miːm/) comprises any idea or behavior that can pass from one person to another by learning or imitation. Examples include thoughts, ideas, theories, gestures, practices, fashions, habits, songs, and dances. Memes propagate themselves and can move through the cultural sociosphere in a manner similar to the contagious behavior of a virus.
Richard Dawkins coined the word "meme" as a neologism in his book The Selfish Gene (1976) to describe how one might extend evolutionary principles to explain the spread of ideas and cultural phenomena. He gave as examples melodies, catch-phrases, beliefs (notably religious belief, clothing/fashion, and the technology of building arches).
Something very interesting to me is that the word for self-replication is a shortened form of the Greek word mimeme -- which looks a lot like Mini-Me!
So that's a meme, but basically in internet jargon basically in internet-jargon it means like a game that people play on blogs where one person posts something and then their friends do the same and so on and so forth.