Seasoning is just oil baked onto cast iron through a process called polymerization. It gives your cookware that classic black patina. Seasoning forms a natural, easy-release cooking surface and helps prevent your pan from rusting.

- Lodge (as I understand it, they're the gold standard for cast iron cookware)

In the case of non-stick stuff, it's less that they're seasoned with PFAS and more that they don't need seasoning because they have PFAS (at least in theory).