Repository

From Zodipedia

A software repository is a storage location from which software packages may be retrieved and installed on a computer or, in this case, on an iPhone or iPod Touch.

The sources you add to Cydia are repositories.

[edit] Repositories

• ZodTTD Public Repository : http://www.zodttd.com/repo/cydia/

You don't have to add it manually, it's preinstalled in Cydia.