A explicit proposal to contract which, if accepted, completes the contract and binds both the person that made the offer and the person accepting the offer to the terms of the contract.
An offer (see sample ad re "offer", pictured, directed exclusively at students) is the initial spark of a contract; it is the seed of a contract.
Lawyers and law professors, in the legal science of contract law, will refer to the offeror and offeree as in: the offeror offers the offeree the offer.
See also acceptance.
Offers and related terms are discussed extensively in the Contract Law section.