pardon my ignorance, but what exactly does "meme" stand for?
It's a made-up word combining "mental" and "gene." It's an inheritable or acquirable cultural social trait that, like genes, might make the bearer more likely or less likely to survive. The latter typically get removed from society fairly quickly, while the former are propagated from generation to generation, occasionally mutating.
What does it mean, or how was the word coined?
It means a self-contained "package" of ideas/beliefs/information that gets passed around from brain to brain, propagating itself kind of like a virus spreading through a population.
If I recall correctly, it was coined from the term "memory gene", since their propagation, "mutation", survival, etc. have a number of parallels with the way that various genes arise, change, and propagate via biological evolution. For example, as an idea makes the rounds, some copies of it will change, either through not being described accurately when being passed from person to person, or by intentional adjustment by one of the peoplel who acquired it and then passes it on -- so after a while, there will be various versions of the meme out there in the public sphere, and a kind of competition ensues, like "survival of the fittest". The ones which are more effective at having themselves adopted by people's minds will proliferate, and the ones which aren't as effective will die off (go extinct). The parallels aren't 100% perfect, of course, but there are enough similar processes at work that the spread, change, rise, and fall of some kinds of ideas follow patterns of behavior similar to that of how biological evolution results in changes in gene complexes.
It's also interesting to note that the success of a meme doesn't necessarily depend on whether it's true or not. For example, a meme which contains, as a package, beliefs that include "you must continue to believe me or horrible things will happen to you", and "you must get others to believe me also, whether they want to or not", as well as a few components that appeal to people's deep wants and fear, will spread virulently even if it's 100% false. Now consider Islam as a meme...