From The Jargon File (version 4.4.7, 29 Dec 2003) :
meme
/meem/, n.
[coined by analogy with ?gene?, by Richard Dawkins] An idea considered as a
replicator, esp. with the connotation that memes parasitize people into
propagating them much as viruses do. Used esp. in the phrase meme complex
denoting a group of mutually supporting memes that form an organized belief
system, such as a religion. This lexicon is an (epidemiological) vector of
the ?hacker subculture? meme complex; each entry might be considered a
meme. However, meme is often misused to mean meme complex. Use of the term
connotes acceptance of the idea that in humans (and presumably other tool-
and language-using sophonts) cultural evolution by selection of adaptive
ideas has superseded biological evolution by selection of hereditary
traits. Hackers find this idea congenial for tolerably obvious reasons.