e-legal lesson

The former may refer either to an informal arrangement with no consideration (e.g., a “gentlemen’s agreement”) or to a formal legal arrangement supported by consideration. Contract is used only in this second sense.
The distinction applies also with the verbs agree and contract. The intended sense of agree(ment) is usually clear from context.

In our next e-Legal Lesson, we’ll explore the prepositions that go with the verb AGREE.