When a project is finished and you no longer need to perform bookings on it, you may archive it.
To archive a project, go to the Projects list > click the Archive icon 
Please note that:
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Projects with bookings in the future cannot be archived
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An archived project is no longer available in the Planner Board
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Past bookings from an archived project are read-only
- To reactivate an archived project, go to Archived Projects list and click Reactivate next to the project you want to unarchive