The traditional contract law rule is that an acceptance must be the mirror image of the offer. Attempts by offerees to change the terms of the offer or to add new terms to it are treated as counteroffers because they impliedly indicated an intent by the offeree to reject the offer instead of being bound by its terms.
Offer verb (AGREE TO GIVE) to ask someone if they would like to have something or if they would like you to do something: + two objects I feel bad that I didn't offer them any food/offer any food to them. She was offered a job in Paris. Can I offer you (= would you like) a drink?
For such an offer to be valid, it must have the clear intention of the offeror; it must be definite; and communication should be with the offeree. Definite terms must be present, and there must be unilateral termination of its openness until accepted or revoked. Terms must be precise and certain.
An acceptance is a final and unqualified expression of assent to the terms of an offer. Again, there must be an objective manifestation, by the recipient of the offer, of an intention to be bound by its terms. An offer must be accepted in ance with its precise terms if it is to form an agreement.
Say for example A offers to buy B's car for rupees two lacs and B accepts such an offer. Now, this has become a promise. When the proposal is accepted and it becomes a proposal it also becomes irrevocable. An offer does not create any legal obligations, but after the offer is accepted it becomes a promise.
A specific offer, on the other hand, is only made to specific parties, and so only they can accept the said offer or proposal. They are also sometimes known as special offers. Like for example, A offers to sell his horse to B for Rs 5000/-. Then only B can accept such an offer because it is specific to him.
For a contract to be binding it needs to satisfy four principles, offer, acceptance, consideration, and the intention to create legal relations. Generally, the law believes that an agreement is made when one party makes an offer and the other party accepts it.
For an offer to be valid, it must be communicated effectively to the offeree, contain definite terms, and show a clear intention to create legal obligations.
In Short. A valid offer must be clear, communicated and made with the intention of creating legal relations. Acceptance must be unconditional, timely and communicated. Duress, capacity and mutual conduct can affect contract validity. Silence may count as acceptance in specific situations.