Mix design
The documented recipe for a batch of concrete: the quantity of each ingredient per cubic yard, plus the strength, slump, and air content it is expected to deliver.
What does mix design mean?
A mix design is developed and tested by the producer, then assigned a number that gets ordered like a part number. It balances competing goals, since the changes that improve workability often hurt strength and the changes that improve strength often hurt finishability. Changing anything at the jobsite, most commonly by adding water, means the concrete placed is no longer the concrete that was designed and tested.
In practice
On commercial jobs the mix design is submitted for approval before the first truck rolls; on residential work it is usually just a number the dispatcher recognizes.