Contracts

An offer is a manifestation of present willingness to enter a bargain, made so as to justify the offeree's understanding that assent will conclude it; it must be sufficiently definite and communicated to the offeree.

An offer must create a reasonable understanding (power of acceptance) that the offeree's assent will conclude the bargain; secret/unexpressed intent is irrelevant — assent is judged objectively.

Advertisements are generally invitations to deal (solicitations), not offers, unless they are sufficiently definite — specifying quantity and identifying who may accept (e.g., 'first come, first served').

An offer terminates by lapse at the end of the time stated in the offer, or if none is stated, after a reasonable time under the circumstances.

A revocation terminates the offer and is effective upon receipt by the offeree, and may occur any time before acceptance (the offeror is generally free to revoke unless the offer is irrevocable).

Yes — an offer is revoked if the offeree learns from a reliable source that the offeror has taken definite action inconsistent with an intent to contract (e.g., selling the item to another).