It is self reported according to the US census recognized racial categories: white, black, asian, native American/Alaskan, native Hawaiian or Pacific islander, and other (or two+ categories). Hispanic/latino identification is a separate box you check for reasons that are hard to explain without going over decades of bureaucratic decisions.
> US census recognized racial categories
Thank you for a googleable term.
Are there any guides on how to decide which "race" you are? Because I cannot imagine that everyone knows exactly which part of the earth all of their ancestors originate from.