Licensing is a legal act. In licensing, a licensor grants a certain portion of the rights to the licensee. This does not mean a complete transfer of rights. The granting becomes effective when the both parties have agreed upon the terms. The copyright holder usually specifies in the licensing terms which rights the licensee can have, how the licensee can make use of the work licensed, in which region or territory the work is licensed, the duration of the license, and so on. That is left out of the licensing terms is regarded as unlicensed, and therefore the licensing terms should be as well thought and detailed as possible. Licenses are most often divided into two categories, exclusive and non-exclusive (please refer to “Exclusive/Non-Exclusive License”), or by the criterion whether the licensee can sublicense. In contrast to transfer, which changes the copyright holder, licensing simply permits another person to use the work, and the licensor still holds the copyright.