These questions are about Linux in general – NOT specific to a particular distribution. If the question just happens to be in a Linux environment, please specify your Linux distribution in the body of your question, but do NOT use the “linux” tag.
The word “Linux” is commonly used to refer to an operating system built around the Linux kernel. This operating system includes many other components, notably from the GNU project, so the term GNU/Linux is preferred. This operating system can also be run without the Linux kernel, and is often, confusingly, still referred to as Linux.
There are many different GNU/Linux distributions (see distros), including more or less the same programs but with different installers (see system-installation), package managers (see package-management), and other customizations. Examples of common distributions are: debian, ubuntu, centos, fedora, arch-linux, linux-mint, rhel, and opensuse.
Use this tag for questions that are specific to Linux-the-operating-system (GNU/Linux), such as hardware support, networking setup, filesystems, etc. Most questions should have other tags to identify the area of interest, e.g., sound, console, iptables, proc, partition, etc.
The Linux kernel is used in some non-unix-like embedded operating systems, the best known being Android. These operating systems are off-topic here (you can ask questions about using Android on Android Stack Exchange).