Who is a prime vendor? It is a single large supplier [vendor] who procures goods and services from different sources for redistribution to a customer within a geographical area. Prime vendors usually purchase and store items required by the customer from a cluster of pre-approved suppliers, referred to as ‘preferred suppliers’.
A customer places purchase orders with the prime vendor as and when required, subject to contract clauses. The prime vendor is responsible for fulfilling all the orders...
https://www.marineinsight.com/maritime-law/prime-vendor-program-logistics-explained/