Understanding the Linux kernel release process
According to the Linux kernel release model, there are always three types of active kernel release: mainline, the stable release, and the Long-Term Support (LTS) release. First, bug fixes and new features are gathered and prepared by subsystem maintainers and then submitted to Linus Torvalds in order for him to include them in his own Linux tree, which is called the mainline Linux tree, also known as the master Git repository. This is where every stable release originates from.
Before each new kernel version is released, it is submitted to the community through release candidate tags, so that developers can test and polish all the new features and, most importantly, share feedback. During this cycle, Linus will rely on the feedback in order to decide whether the final version is ready to be released. When he is convinced that the new kernel is ready to go, he makes (tags it actually) the final release, and we call this release stable...