Every project in Zephyr (as created by Project
Setup) consists of releases (or iterations, versions etc.) and on
creating a new project, a default release labeled "Release 1.0"
is created. This can be easily renamed in the Release Setup application.
Selecting a release in the list or by clicking "Add" opens the lower half of the window to allow adding a Release Name, a Start Date and an End Date and a Description. Only the first two are mandatory. Also, the Start Date of a release has to be after the start date of the Project (as created by Project Setup).
By creating a new Release, the following things happen:
A Release space is created in that particular project as indicated by a tab in the Lead and Tester Desktops
Everything contextual around that release is created automatically - Requirements, Test Case Repository, Execution Assignment & Scheduling, Metrics, Project Dashboard, Documents etc.
You can immediately switch tabs to the new Release and start using it.

You can hide or suppress certain release by clicking on the "Hide" checkbox for that release. By doing so, the following things happen:
1. The tab for that release does not show up in any user's Desktop
2. The tab for that release does not show up in the Project Dashboard
3. Access to all the testcases are still available via the Global tree in TCR and TCC
4. Access to read-only execution statuses are still available via the Global tree in TCE
No data is deleted.
This feature is very useful if you have a large number of releases/sprints/iterations and only a few are currently active.