A license (American English) or licence (Commonwealth English) is an official permission or permit to do, use, or own something (as well as the document of that permission or permit).
A license is granted by a party (licensor) to another party (licensee) as an element of an agreement between those parties. In the case of a license issued by a government, the license is obtained by applying for it. In the case of a private party, it is by a specific agreement, usually in writing (such as a lease or other contract). The simplest definition is "A license is a promise not to sue", because a license usually either permits the licensed party to engage in an illegal activity, and subject to prosecution, without the license (e.g. fishing, driving an automobile, or operating a broadcast radio or television station), or it permits the licensed party to do something that would violate the rights of the licensing party (e.g. make copies of a copyrighted work), which, without the license, the licensed party could be sued, civilly, criminally, or both.