market segregation based business models no relation license
Multi-licensing is the practice of distributing software under two or more different sets of terms and conditions.  This may mean multiple different software licenses or sets of licenses.  Prefixes may be used to indicate the number of licenses used, e.g. dual-licensed for software licensed under two different licenses.
When software is multi-licensed, recipients can typically choose the terms under which they want to use or distribute the software, but the simple presence of multiple licenses in a software package or library does not necessarily indicate that the recipient can freely choose one or the other. In some cases, especially when the software has multiple origins, all the accompanied licenses apply at the same time. The applicability of the different licenses has to be individually checked. The distributor may or may not apply a fee to either option.  The two usual motivations for multi-licensing are license compatibility and market segregation based business models.License compatibility
A second use of multi-licensing with free software is for license compatibility, allowing code from differently licensed free software projects to be combined, or to provide users the preference to pick a license.
Examples include the source code of Mozilla Application Suite and previously Mozilla Thunderbird and Mozilla Firefox, that have used tri-licensing under the Mozilla Public License (MPL) 1.1, GNU General Public License (GPL) 2.0 or GNU Lesser General Public License (LGPL) 2.1 before the latter upgraded to GPL-compatible MPL 2.0, making the tri-licensing unnecessary. Other examples are Perl, which is dual-licensed under the GPL or Artistic License, and Ruby, whose license contains explicit GPL dual licensing.
no relation