From The Free On-line Dictionary of Computing (13 Mar 01) [foldoc]:

  meme

      /meem/ [By analogy with "gene"] Richard Dawkins's
     term for an idea considered as a {replicator}, especially with
     the connotation that memes parasitise people into propagating
     them much as viruses do.

     Memes can be considered the unit of cultural evolution.  Ideas
     can evolve in a way analogous to biological evolution.  Some
     ideas survive better than others; ideas can mutate through,
     for example, misunderstandings; and two ideas can recombine to
     produce a new idea involving elements of each parent idea.

     The term is used especially in the phrase "meme complex"
     denoting a group of mutually supporting memes that form an
     organised belief system, such as a religion.  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 become
     more important than biological evolution by selection of
     hereditary traits.  Hackers find this idea congenial for
     tolerably obvious reasons.