n. soft, European cheese similar to cream cheese
No, it's not a subatomic particle. The first time I heard quark mentioned in a gastronomic context I was confused; what was this - a crossover from long forgotten physics lectures? It turns out that quark is a very soft, mild cheese that is common in Europe but especially in Germany. It is a simple pot cheese like ricotta, queso blanco, or paneer, traditionally created by leaving the cheese hanging in a cloth and letting the whey drip off.
The German word quark, however, was used in James Joyce's book Finnegans Wake and may indeed have inspired the name of the subatomic particle. Hmm. Particle physics and cheese...