Lowest Responsible Bidder
The award standard in competitive bidding. Two separate tests hide inside it: whether the bid met the specification, and whether the bidder can actually perform.
The phrase is usually heard as a complaint about being forced to buy the cheapest thing. It is more precise than that, and the precision is useful.
Responsive asks whether the bid conforms to what was asked for. A bid that omits a required item or changes a term is non-responsive and can be rejected regardless of price. Responsible asks whether the bidder is capable of delivering: financial standing, capacity, past performance, service support.
So the standard is not lowest price. It is lowest price among bids that met the specification, from a bidder able to perform. Both tests are real, and both are more defensible before an award than after one.
The practical implication for a fleet is the same as everywhere else in public procurement: the leverage sits upstream. A requirement that is not in the specification cannot be enforced through the responsibility test just because everyone knows it matters.