I think the word “meme” is an invention of Richard Dawkins. It’s used to designate a unit of culture that can propagate in a manner analogous to genes. Like genes, memes are coded with methods that encourage their own reproduction, can mutate and compete with other memes within their (cultural) environment. The textbook examples of memes include the chain letter (email) and urban legends.

I find it particularly useful to think of religions as memetic complexes, with Christianity and Islam as the two most successful ones.

Meme!