A proposal is an essential marketing document that helps cultivate an initial professional relationship between an organization and a donor over a project to be implemented. The proposal outlines the plan of the implementing organization about the project, giving extensive information about the intention, for implementing it, the ways to manage it and the results to be delivered from it.
A Concept Note is perhaps the shortest expression your project idea given on paper to a donor. It is usually requested by the donor in situations where no proposals have been solicited from NGOs. Most of the donor agencies prefer to understand the project through a Concept Note rather than a full-fledged proposal.
You can learn more about proposal writing at https://freeresources.fundsforngos.org/#proposalwriting