Meme is a term coined by Richard Dawkins in imitation of the word gene. It indicates a unit of reproduction in the world of ideas. Memes are subjects to

1. Reproduction (they are copied),
2. Mutation (the copying process isn't perfect) and
3. Selection (the probability of reproduction is influenced by properties of the meme)

and hence they undergo evolution.

You can find some Memetics Papers here: http://users.lycaeum.org/~sputnik/Memetics/