A meme is any concept or fragment of idea that is passed on willingly by hosts, under the impression that it is for their own benefit.
While a virus must take some form of control, duping the host or having them be unaware of its presence, a meme is simply a cool idea.
In our current world order, memes are an excellent way to control the populace. For any uncertainty, introduce a meme that makes the person repeating it seem as if they have an answer to the uncertainty. Thus they'll pass it on, thinking themselves empowered.