Meme - what is it?

I just learned of this term today, in the context of the internet. By definition meme is how an idea transfers from one mind to another. Apparently, this concept is now being used by companies to research how quickly a bit of advertising can move through the internet. The idea is to plant a meme and monitor it's movement and growth.

We've all seen something similar to this in the form of those email forwards; usually it's a joke, a nice story or a photo. Not only do these seem to traverse the entire internet (in many languages), but they also seem to make the rounds over and over again (remember, the largest part of the internet is email). I don't pretend to understand the dynamics of how all this happens but I've often noticed how a newbie email user often is susceptible. They build their address book and start forwarding email with abandon. They honestly feel they think I have not seen this really cool story before and if I don't forward it to ten others, I'm some sort of scum.

Much to their consternation, they're getting loads of spam...