A permanent map, also called a perm map, protect map, or locked map, is a map that cannot be removed. Therefore, you cannot vote for them. These maps will not appear in vanilla rooms.
Unlike official maps, permanent maps occur with the same rarity as regular user made maps.
If you own a permanent Map and open it in the Map Editor, you aren‘t allowed to change it and there is a banner which reads "This map is now permanent. You cannot change it."
In-game, you can recognize a permanent map by looking at the creator's name in the top left corner of the map. If the map is permanent, there will be a lock icon next to the name.
A map can be made permanent by taking part in the Map Making Contest.