Any individual mod can add a "Great Question" flair like we do with any other flair, but that said we sometimes discuss with other mods first in a SUPER SEKRIT BACKROOM we have. It's meant as a way to draw attention to a question that we find particularly interesting or useful (e.g., not another question about what Hitler thought about _____).

Just to add to the above, this is fleshed out a little bit more here in the announcement about the new flair.