Raw or bare cast iron has no protective coating, which makes the cookware susceptible to rusting. Of course, many people still cook with raw cast iron, but these pieces require seasoning before use.
Pre-seasoned cast iron has a protective coating on it that's derived from natural materials such as coconut oil or silicone. While pre-seasoned cast iron can be used out of the box, it requires occasional seasoning to prevent rust.
Enamel cast iron is coated with enamel paint. It does not require seasoning unless the cookware has exposed areas (generally around the rim and lid), which are very low maintenance. Learn more here.