It is generally defined as a benefit conferred or a detriment incurred at the behest of the other party. Consideration is more than a mere gift. More than morals. It represents a mutual interest. It is also referred to a quid pro quo , what for what, and the benefit of the bargain.
Exceptions are prevalent such as common law sealed instruments and promissory estoppel.
The Uniform Commercial Code also provides for firm offers, modifications, etc. without the requirement of consideration. As stated contractual agreement requires mutuality. Some years ago Steve Allen hosted a PBS television program in which historical figures portrayed by actors interacted over one hour. For example, Cleopatra, Benjamin Franklin, Groucho Marx and Atilla the Hun might discuss today's hot topics over a hot cup of coffee. It is an affirmative response to the offeror's offer.