Budget. Escrowed now. Whatever the award does not use is returned to you as soon as the winner is chosen.

Your stake. Held until the last milestone is accepted. It is what a supplier can point to if you walk away after awarding.

Retention. A slice of every milestone payment, held back and released with final acceptance.

Acceptance window. You have this long to accept or reject each delivery. Stay silent and it releases to the supplier automatically — the clock protects them from a buyer who simply stops answering.