All it means is that the reefer unit on the truck works the way it supposed to work. The truck must have a way to record events (opening of doors, out of range temps) and temperatures either on demand or at regular intervals and print them out.
The validation of the system is to ensure that the system operates within parameters set by the manufacture and the monitor equipment properly monitors the temps and events. They testers have a validation script that they follow to ensure consistency.
The carrier must follow the current
Good Manufacturing Practice or cGMP that all food and Phrama companies abide by in regards to transportation of specific products but it is not limited to these industries alone, other high tech companies also follow the cGMP and other cGxP rules when transporting products.
I don't know if FedEx has the TM in T-val but the words Temperature Validation is used in the Phrama industry a lot.