definitions

A meme is any unit of cultural information, such as a practice or idea, that is transmitted verbally or by repeated action from one mind to another.

A meme is defined within memetic theory as a unit of cultural information, cultural evolution or diffusion that propagates from one mind to another analogously to the way in which a gene propagates from one organism to another as a unit of genetic information and of biological evolution. Multiple memes may propagate as cooperative groups called memeplexes (meme complexes). Via Wikipedia.

Biologist and evolutionary theorist Richard Dawkins coined the term meme in 1976. He gave as examples tunes, catch-phrases, beliefs, clothing fashions, ways of making pots, and the technology of building arches.

Meme theorists contend that memes evolve by natural selection similarly to Charles Darwin's theory of biological evolution through the processes of variation, mutation, competition, and inheritance influencing an organism's reproductive success. So with memes, some ideas will propagate less successfully and become extinct, while others will survive, spread, and, for better or for worse, mutate. Memeticists argue that the memes most beneficial to their hosts will not necessarily survive; rather, those memes that replicate the most effectively spread best, which allows for the possibility that successful memes may prove detrimental to their hosts.