Archive (take offline, keep the files)
Click Archive on a project. The link stops working straight away, and the project no longer counts towards your live-project limit. Restore it from Archived Projects whenever you like, as long as you have a free project slot on your plan.
Delete
Click Move to trash. The link stops working and the project goes to Deleted Projects, where it stays for 7 days. During that time you can restore it. After 7 days, or if you choose Delete forever, the files are permanently removed.