A call-off contract is an individual order placed under an existing framework agreement or dynamic purchasing system. The overarching agreement sets who may supply and on what terms; the call-off is the actual, binding contract for a specific piece of work.
Call-offs are awarded in one of two ways. Direct award goes to a framework supplier without further competition, usually by applying a pre-agreed ranking or price list. A mini-competition invites some or all of the framework suppliers to bid against a specific requirement, scored on criteria already set out in the framework.
This distinction matters more than it first appears. Winning a place on a framework is not winning work, it is winning the right to be asked. Suppliers regularly celebrate an appointment and then receive nothing for a year because they treated the framework as the finish line. Once appointed, the job changes: stay visible with the buyers entitled to use it, respond quickly to mini-competitions, and treat each call-off as a real bid with real competitors, because that is exactly what it is.