It's a pretension adopted from the wine industry to justify charging more money. It just means having a flavor reminiscent of chocolate, and maybe a mouthfeel as well. It suggests that the coffee is complex, of course delicious, unique, and is the result of a magical synergy of earth, farming methods, climate, you name it. Mostly, it's all bullshit. Having said that, a really good cup of coffee does stand out as being a whole lot more pleasurable, to me, than the cheap stuff. And if I had to describe why it's so delicious to me, I might come up with some bullshit too.