From Lostpedia

Guest stars are actors who have speaking roles. In some cases their lines are cut during editing, but they are still required to be credited.

1. Background extras, stand-ins, and stunt doubles are not included in this list.
2. Actors portraying recurring roles or Major Roles (e.g. Danielle Rousseau) are not listed here, and should be categorized as Category:Cast.
3. Non-speaking roles, characters that are specified in the script but not given lines, are categorized as Category:Background.

The guest stars category is a subcategory of Category:Cast.