This word showed up in popular usage in Neal Stephenson’s novel Snowcrash. I’ve seen it come up a lot as I was surfing the web.
So it means: an idea that spreads like a virus. (?)
noun: Biology- an element of behaviour or culture passed on by imitation or other non-genetic means. from the Compact OED
noun: an idea, behavior, style, or usage that spreads from person to person within a culture