All projects have two main statuses, inactive and active. An inactive project (a.k.a. archived) and all tasks related to the project will be hidden from the workspace views.
Navigate to Settings.
Open Project settings.
Note these two options under the status dropdown. Active/Inactive.
You may create as many project statuses as you like, customize it's color and text, as well as whether they are in either Active/inactive states.
For example, a project may have several different states that should be treated as inactive. Such as above where we have both Canceled and Completed to be treated as inactive.