In Martin's A Dance of Dragons, greyscale is described as a contagious disease with potentially fatal consequences. The condition turns the skin to a stone-like texture and becomes cracked.

A major character on "Game of Thrones" recently contracted a nasty disease that turns your body to stone, and he's now in search of a cure. Greyscale, as it is known, has been referenced a number ...

We still don't know that much about the disease or many other people who suffer from it, but it's caused fans to wonder if the Targaryens are immune to greyscale. It's a good theory, and if true ...

who once survived Greyscale — a disease not unlike leprosy, if leprosy turned you into a statue person. But in the final moments of the episode, after it seemed that Tyrion would be the one ...