The following information is from Wikipedia and serves as a basic history lesson on Linux, Open Source, GPL and the Linux Kernel.
What is Linux?
According to Wikipedia, Linux is a generic term referring to Unix-like computer operating systems based on the Linux kernel. Development is one of the most prominent examples of free and Open Source software collaboration; typically all the underlying source code can be used, freely modified, and redistributed, both commercially and non-commercially, by anyone under the terms of the GNU GPL.
The name "Linux" comes from the Linux kernel, originally written in 1991 by Linus Torvalds. The rest of the system usually comprises components such as the Apache HTTP Server, the X Window System, the GNOME and KDE desktop environments, and utilities and libraries from the GNU Project (announced in 1983 by Richard Stallman). Commonly-used applications with desktop Linux systems include the Mozilla Firefox web-browser and the OpenOffice office application suite. The GNU contribution is the basis for the Free Software Foundation's preferred name GNU/Linux.
What is Open Source?
Open Source is an approach to the design, development, and distribution of software, offering practical accessibility to a software's source code. Some consider open source as one of various possible design approaches, while others consider it a critical strategic element of their operations. Before open source became widely adopted, developers and producers used a variety of phrases to describe the concept; the term open source gained popularity with the rise of the Internet, which provided access to diverse production models, communication paths, and interactive communities.
What is GNU GPL?
The GNU General Public License (GNU GPL or simply GPL) is a widely used free software license, originally written by Richard Stallman for the GNU project. The GPL is the most popular and well-known example of the type of strong copyleft license that requires derived works to be available under the same copyleft. Under this philosophy, the GPL grants the recipients of a computer program the rights of the free software definition and uses copyleft to ensure the freedoms are preserved, even when the work is changed or added to. This is in distinction to permissive free software licenses, of which the BSD licenses are the standard examples.
What is the Linux Kernel?
The Linux Kernel is an operating system Kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software. The Linux Kernel is released under the GNU General Public License version 2 (GPLv2) plus proprietary licenses for some controversial BLOBs and is developed by contributors worldwide. Day-to-day development takes place on the Linux Kernel mailing list.
Citation: Wikipedia.