National Highway Traffic Safety Administration (NHTSA)
The federal agency setting vehicle safety standards and administering recalls. Its definitions are the ones behind most vehicle classifications a fleet uses.
NHTSA writes the Federal Motor Vehicle Safety Standards that manufacturers build to, and runs the recall system.
Recalls are the part a fleet handles operationally, and at fleet scale they need a process rather than a reaction: knowing which units are affected, getting them scheduled, and being able to show later that they were completed. A fleet that cannot answer whether an open recall is outstanding on a particular unit has a records problem before it has a safety problem.