Linux distribution
Linux initially only had a kernel, which was very difficult for the majority of users. In order to reduce the difficulty of deployment, there was a release. Linux distributions can be roughly divided into two categories, one is the distribution maintained by commercial companies, and the other is the distribution maintained by community organizations. The former is represented by the famous Redhat (RHEL), and the latter is represented by Debian. 
There are currently three mainstream distributions, Redhat, Debian and SUSE. There are many branches based on these releases.
Branch based on Rehat distribution
Fedora: Red Hat’s test field, using the latest technology to test.
Centos as the upstream version of RHEL : It was maintained by the open source community in the early days. As a downstream version of RHEL, it was known for its stability and reliability and was later acquired by Red Hat. The original support plan will not be changed. After an announcement in December 2020, Centos8 will support until the end of 2021. Later, the Centos distribution became a midstream version between Fedora and RHEL.
RHEL: As a paid version of Red Hat, it applies stable applications and fast updates to fix vulnerabilities. It is the preferred version for many large commercial units.
Branch based on Debian distribution
Debian has maintained at least three release versions: stable, testing and unstable.
Stable version (stable) The
stable version contains the latest official Debian package.
As the official release version of Debian, it is the version we recommend to users first.
The current stable version of Debian is version 10, and the development code is buster. The original version is 10, which was released on July 6, 2019, and its update 10.9 was released on March 27, 2021.
The beta version
contains packages that have not been included in the stable version for the time being, but they have entered the candidate queue. The biggest benefit of using this version is that it has more versions of newer software.
The current beta version is codenamed bullseye.
The unstable version
contains the current development work of Debian. Usually, only developers and those who like to live a thrilling life choose this version. It is recommended that users who use the unstable version subscribe to the debian-devel-announce mailing list to receive notifications about major changes, such as upgrades that may cause problems.
The version code of the unstable version is always called sid.
Ubuntu:
Ubuntu is a Linux operating system based on desktop applications. Its name comes from the word "ubuntu" in Zulu or Hausa in southern Africa, meaning "humanity" "I exist because of everyone's existence", It is a traditional value in Africa. Ubuntu is based on the Debian distribution and the Gnome desktop environment. This release will use the latest kernel and software, allowing users to develop and use new features more quickly.
SUSE
SUSE Linux was originally based on Slackware Linux and provided a product with a complete German user interface. openSUSE has always named its version with a different green hue. Therefore, openSUSE releases are called Teal, Emerald, etc., and long-term releases are called evergreen. It is a very popular system in Europe. Only some companies in China will use SUSE as a server operating system.
The above several releases are just the more popular versions among many releases, and there are many versions, which have many advantages and features.