What does "testing server" mean in the Latest Changes list?

Some changes in Latest Changes have a “testing server” badge next to them.

These are changes that were released to the testing server first but are now available on the main site as well.

In the above screenshot the change from “4 hours ago” was released only to the testing site and then a few hours later (ie: the “22 minutes ago” change) it was made available on the main site as well.

If you’d like to help test new features before they go out to the main site see the help article at: How can I help test new features on the testing site?