What is the term for an oral or written agreement to do or not to do a certain thing?

The term that best fits the description of an oral or written agreement to do or not to do a certain thing is a contract. A contract is a legally binding agreement between two or more parties that outlines the specific terms and conditions of the arrangement. It can be oral or written, though written contracts are often more enforceable due to their clear documentation of the terms agreed upon.

In the context of real estate, contracts are crucial as they provide the framework for transactions, defining the rights and responsibilities of each party (such as buyers and sellers, or landlords and tenants). Understanding the nature of contracts is fundamental in real estate transactions, as it protects the interests of the parties involved and ensures that commitments are formalized.

While the other options, such as agreement, understanding, and commitment, hint at the concept of mutual accord, they do not carry the same legal weight as a contract. An agreement may not be legally enforceable, an understanding typically lacks specificity and detail, and a commitment is a promise but does not inherently imply a legal obligation as a contract does. Thus, 'contract' is the most accurate term for a legally binding agreement governing actions or behaviors.