We see "memes" all over the place now, but what does "meme" really mean? Well, originally it was a genetic term coined by Richard Dawkins in 1976 book, The Selfish Gene. In genetics it means that one thing imitates another, but is slightly different. It originates through a repeated mutation. So, with the advent of Internet Memes, what we have seen is typically a picture with a slogan, and it gets slightly altered and then propagated throughout the Internet, sometimes "virally" (another biological comparison).
My favorite Catholic Meme for today is this one:
This is, of course, a "mutation" of the Dos Equis beer commercial.