A software license is a legal agreement that binds software developers with specific conditions they must follow. When a software publisher owns a piece of software, an end-user needs a license to operate it. Usually, the software license is a long string of letters and numbers; this essential data is called a product key. A licensee enters the key as one of the conventional software installation steps. Without a key, you can’t access the software because it proves you are compliant with the owner’s requirements. The license also dictates whether you can explore, modify, copy, and redistribute the software’s source code; each software license has its unique set of stipulations.