Limited means the instance has done something not quite to the level of total defederation, but still limits the presence of Threads users. For example, making it so you can only see a Threads user if you actively search for and follow them, removing all Threads content from the global feed by default, preventing Threads users from following your users, etc.

"Fedipact" means that the admin of that instance has signed on to the informal agreement of the same name between instances that pledged to defederate from Threads preemptively.