A sales proposal or business proposal is a document that a company delivers to potential clients outlining the benefits of its product or service as well as the particular issue it may help resolve.
A strong sales pitch serves as an example of why a client should cooperate with (or purchase from) your business. A brief proposal should ideally communicate to potential clients that you are aware of their problems, have a solution for them, and are available and willing to assist.
Source: https://www.elatesoft.com/blog/how-to-write-a-sales-proposal-and-win-more-clients/