What is r31?

It appears that "r31" is a very broad and general term that could refer to many different things. Without more context, it is difficult to determine exactly what you are referring to.

For example, "r31" could refer to a model number of a product, a type of software, a code or classification system, a scientific study, a medical diagnosis, a specific location or any number of other things.

If you could provide more specific information or context about what "r31" is in reference to, I would be happy to give you more detailed information.