Simply put, a contract comprises different provisions or terms that give the contracting parties rights and responsibilities. Contract terms create an obligation on one or all the parties; when a party doesn't comply with a term, there is a breach of contract.
FAR 16.306. It provides for two types of CPFF contracts: the Completion type, which has a “definite goal or target and specifies an end product,” and the Term type, which “obligates the contractor to devote a specified level of effort for a stated time period.”