Proposal and its acceptance are the two essential elements of a contract. When a proposal is accepted, it leads to the formation of an agreement between the parties involved. Let's understand the meaning of proposal and its acceptance.

Proposal:

- A proposal is a statement made by one party to another party, expressing the willingness to do or abstain from doing something.
- It is a preliminary offer made with an intention to create a legal obligation.
- A proposal becomes complete when it is communicated to the person to whom it is made.

Acceptance:

- Acceptance is an expression of assent to the terms of the proposal.
- It is a positive response to the proposal made by the other party.
- Acceptance must be communicated in the manner prescribed in the proposal or in a reasonable manner.

Proposal + Acceptance = Promise:

- When a proposal is accepted, it leads to the formation of an agreement between the parties involved.
- The agreement creates a legal obligation on the parties to perform their respective promises.
- The promises made by the parties constitute the terms of the agreement.

Proposal + Acceptance + Consideration = Contract:

- A contract is an agreement enforceable by law.
- Consideration is an essential element of a contract, which refers to something of value given by one party to another in exchange for the promise made by the other party.
- Therefore, a contract is formed when a proposal is accepted with consideration.

Conclusion:

Hence, a proposal when accepted becomes a promise, which can further lead to the formation of a contract when consideration is present.

There might be some corrections because correct answer is "promise"