An open source distribution (distro) is a copy of an open source project, created and managed separately from the main project, and independent of other distributions. The open source project from which it is copied is a collaborative development, documentation and testing effort. The projects have a central repository where the source code is developed and shared. Vendors are free to download and copy the source code any time, make modifications, and distribute their version to others under the same open source rules. This becomes their open source distro.
Any given open source project can have many distributions that are derived from it. For example, the Linux project has given rise to distros like SUSE, Red Hat, Ubuntu, CentOS, and many others. But all Linux distros use the same Linux kernel.
Vendors often offer highly tested and stabilized versions of their distros as commercial products, along with services such as support, training and consulting, that make them more suitable for the demands of enterprise customers. However, users can also freely download newer versions of these distros, which are suitable for skilled users who are more tolerant of bugs and do not require high stability. For example, SUSE sells its SUSE Linux Enterprise products and support subscriptions to organizations around the world, but on openSUSE.org anyone can download its latest version of the distro for free.