Learn in the textbookOpen Source Software (OSS) and Licenses
DefinitionGPL (GNU General Public License) is a leading OSS license built on the idea that modified versions carry the same conditions.
ExplanationGPL was written for the software of the GNU Project, and the Linux kernel is among the programs that use it. A GPL program can be used, modified and redistributed freely, but anyone who distributes it, modified or not, must let the recipients obtain its source code and attach the same GPL to it. Someone who only uses a modified version themselves and does not distribute it has no such obligation.
AnalogyIt is like a recipe that says: if you adapt this and hand it on, include your adapted method and attach the same set of rules.
Memory hookThe G stands for GNU, a name that is an acronym of "GNU's Not Unix" and so repeats itself inside its own expansion.