Test Center is a special shard where players can go to test out upcoming changes. Players can manually set their Skills and Stats to whatever settings and combinations they choose on the fly and they can also copy their current characters on their home shard using Character Copy option. Resources, artifacts and many other items are provided for free to facilitate testing as well. Once testing is complete the shard is usually taken down or wiped for the next set of changes.
Test Center is usually listed in the shard selection menu after account login as TC1 and is sometimes referred to colloquially by UO players as "TC".