meme n : a cultural unit (an idea or value or pattern of behavior) that is passed from one generation to another by nongenetic means (as by imitation); "memes are the cultrual counterpart of genes"but in reality tends to take the form of a link to a vaguely amusing web-site, often hosting some kind of quiz or test. The spread of a meme through the blogosphere can often be very rapid. I tend to come across them on planet.debian.org. There is certainly no element of passing from generation to generation!
Some guy is attempting to measure this wildfire phenomena by encouraging people to link to his article on the subject. Join in if you like!