What is the meant by the statement that an offer extended by one party to another can only be accepted if it is "alive?"

Question

Quizplus · Accepted Answer

An offer can only be accepted if it is still available or "alive." This means that the offeror has not revoked or withdrawn the offer, and that the offer has not expired due to a specified time limit or the occurrence of a condition beyond the control of either party. A valid offer does not necessarily have to be an offer to treat, and rejection of a conditional offer does not necessarily make the offer "dead."

What Is the Meant by the Statement That an Offer