All agreements are contract but all contracts are not agreement

Contract: An agreement enforceable by law is a contract. 

Agreement: Every promise and every set of promises forming consideration for each other is an agreement. 

An agreement is termed a contract only when it is enforceable by law. All agreements are not necessarily legally enforceable. It can rightly be said that an agreement has a much wider scope than a contract. For example, agreements are not legally binding are an invitation to dinner or to go for a walk and its acceptance. These are agreements, not contracts.

An agreement need not necessarily be within the framework of law and be legally enforceable. If it is, then it is a contract. A promises B to do physical harm to C whom B does not like and B promises to pay A TK. 1000 to do that, it cannot be termed as a contract because such an act would be against the law. Any agreement of which the object or consideration is unlawful is void and cannot be called a contract.

It would be clear from what has been said so far that an agreement has a much wider scope than a contract. An agreement implies fulfilling some agreed condition. It does not necessarily imply that the stipulated conditions conform to the law and are enforceable by it. It may be said that an agreement is the genus of which contract is the species. It also makes it clear that all agreements are not contracts but all contracts are agreements.