1 : an idea, belief or belief system, or pattern of behavior that spreads throughout a culture either vertically by cultural inheritance (as by parents to children) or horizontally by cultural acquisition (as by peers, information media, and entertainment media) 

2 : a pervasive thought or thought pattern that replicates itself via cultural means; a parasitic code, a virus of the mind especially contagious to children and the impressionable 

3 : the fundamental unit of information, analogous to the gene in emergingevolutionary theory of culture 
- meme pool (n.) : all memes of a culture or individual 
- memetic (adj.) : relating to memes 
- memetics (n.) : the study of memes 

4 : in blogspeak, an idea that is spread from blog to blog 

5 : an internet information generator, especially of random or contentless information 

(Etymology : meme : derived from the Greek mimėma, 'something imitated', byRichard Dawkins in 1976)