5b.2.4 HOW may FOSS be redistributed by licensees?
Permissive FOSS licences place no or minimal requirements on the redistribution of FOSS. Copyright notices, designations of authorship, references to the licence as well as liability waivers must often just be retained. In many cases, copies of the licensed computer program may also only be distributed in the form of object code . This means that the recipients of the redistributed computer program have no further opportunity to edit the computer program in technical terms. Examples of permissive FOSS licences are the free BSD licence and the MIT licence.
In the case of Copyleft FOSS licences, higher requirements are placed on the redistribution of the licensed program than for permissive licences. All notices, etc. must be retained for Copyleft FOSS licences as well. If a licensed computer program is redistributed in an unmodified form, the redistributor must often provide the source code too. Redistribution solely in the form of object code without offering the source code is not permitted.
If a computer program is modified and subsequently distributed, the newly added code must be distributed under the same FOSS licence or under a compatible FOSS licence. This means that the person who has edited the computer program and thus receives their own copyrights must also license these copyrights to all interested parties. Moreover, the source code of the modified computer program must be disclosed. Copyleft is a legal gimmick to keep the distributed original program and the changes made to it accessible to everyone.
The prerequisites or scopes of modification that trigger the obligation to license a modification under the same FOSS licence or under a compatible one, can differ from licence to licence.
Examples for copyleft FOSS licences are the GNU GPL and the GNU LGPL.