Steam key reseller. Some of those stores are above board, and some are not. Fanatical is legit–apparently they’re owned by Focus Multimedia, who started as a budget publisher of PC games. As I understand it, publishers sell keys to retailers like Fanatical, who run bundles and sales to capture audiences looking for deals.
It’s a complicated market, and there are quite a few bad actors. It also just feels weird to buy Steam keys from another store. But along with Humble, Fanatical is probably in the top tier of legitimate sellers.
(We have a thread on the more questionable sides of the reselling practice)