Ubuntu is a Linux distro based on Debian, designed for 64-bit PCs and servers of various CPU types, as well as some 32-bit ARM-based systems. It is designed for both personal and enterprise use, and is available for free for any use, personal or commercial.
The official Ubuntu releases come in at least four different package and kernel configurations (could be called variants, and cited here from the Ubuntu Wiki):
- Ubuntu Desktop - Ubuntu is a complete desktop Linux operating system, freely available with both community and professional support.
- Ubuntu Server - The most popular server Linux in the cloud and data centre, includes five years of guaranteed free upgrades.
- Ubuntu Core - Ubuntu Core is a lean, strictly confined and fully transactional operating system for the Internet of Things (built only using snap packages, without the apt package system).
- Ubuntu Cloud - Ubuntu builds optimised and certified server images for partners like Amazon AWS, Microsoft Azure, Google Cloud Platform, Oracle, Rackspace and IBM Cloud (using special cloud images with optimised kernels for each platform).
Some paid features are available that may come in handy for enterprise users (though Ubuntu may be used for enterprise use freely without those features). Ubuntu Desktop and Server both come with 5 years of community support and software updates.
Ubuntu flavors (such as Kubuntu, Xubuntu, Ubuntu MATE, and others) are simply alternate Ubuntu configurations geared toward a specific use or built around a specific desktop environment. They use the exact same packages as Ubuntu itself, and are based on the Ubuntu Desktop base system.
All Ubuntu flavors are essentially the same as Ubuntu, and therefore receive the same community support and can be used for the same purposes. Ubuntu flavors come with 3 years of community support and software updates.
Ubuntu remixes are similar to Ubuntu flavors, but are not officially recognized as flavors. They may contain packages that are not part of Ubuntu and may use development processes that aren't the same as Ubuntu's. Ubuntu Cinnamon and Ubuntu Unity are two examples of remixes. Remixes are generally relatively close to Ubuntu, but there are no rules in place that say that they have to stay that way.
This results in the possibility for changes to be made that make such systems difficult to support for people who aren't used to the particular quirks of a remix, and so they are not officially supported by Ubuntu support channels like Ask Ubuntu, the Ubuntu Forums, or the Ubuntu support IRC chat. However, a remix's creator may provide their own support channels for their remix.
Due to the fact that remixes generally stay close to Ubuntu, they are good candidates for potentially becoming official Ubuntu Flavors if the developers are willing to go through the process of making their remix an official Ubuntu flavor. At least one remix (Ubuntu Cinnamon Remix) is working on becoming an official flavor.
Ubuntu derivatives technically include all of the above, but also include operating systems that may only be loosely based on Ubuntu, or that may depart far enough from how Ubuntu works as to be considered a distro all of their own. Linux Mint and Pop!_OS are two examples of derivatives.
They are not supported by Ubuntu support channels for the same reason as remixes are not supported, however they may provide their own support channels.