Here's an aesthetic way to think about what a meme is (my favorite way to think about anything):
"MEME The life form of ideas. A bad idea is a dead meme. The transience as well as the spread of ideas can be attributed to the fact that they replicate, reproduce and proliferate at high speed. Ideas, in their infectious state, are memes. Memes may be likened to those images, thoughts and ways of doing or understanding things that attach themselves, like viruses, to events, memories and experiences, often without their host or vehicle being fully aware of the fact that they are providing a location and transport to a meme. The ideas that can survive and be fertile on the harshest terrain tend to do so, because they are ready to allow for replicas of themselves, or permit frequent and far-reaching borrowals of their elements in combination with material taken from other memes. If sufficient new memes enter a system of signs, they can radically alter what is being signified. Cities are both breeding grounds and terminal wards for memes. To be a meme is a condition that every work with images and sounds could aspire towards, if it wanted to be infectious, and travel. Dispersal and infection are the key to the survival of any idea. A work with images, sounds and texts needs to be portable and vulnerable, not static and immune, in order to be alive. It must be easy to take apart and assemble, it must be easy to translate, but difficult to paraphrase, and easy to gift. A dead meme is a bad idea."
On the other hand, this little article about how a meme becomes content embarks from the mainstream and breaks it down by example.
Now you know.
PS: The pizza hut commercial is funnier.