The definition of Acceptance in contract law is under Section 2(b) of the Indian Contract Act, 1872. It states that "when the person to whom the proposal is made gives his assent, the proposal is considered as accepted." This means that when the offeree agrees to the terms of the offer without any modifications, acceptance occurs, transforming the proposal into a promise.

The Indian Contract Act, 1872, provides a framework for acceptance in contract law through several key sections:

• Section 2(b): Defines acceptance as the assent by the person to whom the proposal is made.
• Section 7: Specifies that acceptance must be absolute and unqualified, and it must be expressed in some usual and reasonable manner, unless the proposal prescribes the manner in which it is to be accepted. 

For acceptance to be valid, certain essential features must be present:

1. Unconditional and Absolute: The acceptance must correspond exactly with the terms of the offer without any variations. Any deviation may be considered a counteroffer, not acceptance.
2. Communication to the Offeror: Acceptance must be communicated to the offeror. Mere mental assent or uncommunicated intention does not constitute acceptance. 
3. Prescribed Mode: If the offer specifies a mode of acceptance, it must be followed. If no mode is prescribed, acceptance should be in a usual and reasonable manner. 
4. Within Prescribed Time: Acceptance must be made within the time prescribed in the offer or, if no time is stipulated, within a reasonable time.
5. Knowledge of the Offer: The offeree must be aware of the offer at the time of acceptance. Acceptance without knowledge of the offer is not valid.

The various forms of acceptance can be:

1. Express Acceptance: Communication of acceptance clearly through written or spoken words
2. Implied Acceptance: When acceptance is inferred from the conduct of the offeree or the circumstances, indicating agreement to the offer. 
3. Conditional Acceptance: When the offeree agrees to the offer's terms but with certain modifications or conditions. This typically constitutes a counteroffer rather than acceptance.

Several landmark judgments have shaped the understanding of acceptance in law of contracts Carlill v. Carbolic Smoke Ball Co. (1893): In this English case, the court held that a unilateral offer could be accepted by performing the stipulated act without prior communication. The company's advertisement promising £100 to anyone who used their product and still contracted influenza was deemed a binding offer, and Mrs. Carlill's use of the product constituted acceptance. 

• Brogden v. Metropolitan Railway Co. (1877): The House of Lords held that a contract could be formed through conduct, even if formal acceptance was not communicated. The parties had acted on the terms of a draft agreement, thereby indicating acceptance. 
• Powell v. Lee (1908): This case established that acceptance must be communicated by an authorized person. An unauthorized communication of acceptance does not bind the parties to a contract.

Legal binding contracts require acceptance as their fundamental component to establish the formation process. The acceptance in contract law establishes mutual obligations between parties by showing the offeree's agreement with all offer conditions. The key characteristics along with acceptance types serve to establish clear contractual terms which avoid relationship disputes. Judicial decisions have explained contract acceptance fundamentals while strengthening its essential place in legal contracts.

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