Blanket Contract Law & Legal Definition. Blanket contract is a type of contract that covers a wide range of products and services. It covers a group of products, goods, or services that are identified by the parties to the contract.The contract is for a fixed period.For example, an advertising contract that is not restricted to a particular agency but covers a number of agencies.t covers a group of products, goods, or services that are identified by the parties to the contract. The contract is for a fixed period.