The idea archive is an area to collect and maintain valuable ideas. These ideas are not currently part of the idea process cycle, but are worthy of preservation. These ideas, may not be appropriate today, but can be searched and retrieved at anytime for future needs.
An idea can be archived at any stage by an administrator. The idea will still appear in some smart searches (idea creation for example). Visibility or the archive can be controlled by an admin at admin->modules->archive.
To archive an idea click the settings cog while viewing the idea and select the Archive idea option:
Archiving an idea will lock all user interactions (commenting, voting etc.). An idea can be un-archived at any time.