An operating system made by Valve that comes pre-installed with the Steam client and is designed primarily for gaming. It is also the operating system pre-installed on the Steam Deck. This tag should be used when the question is about a feature unique to SteamOS, or when the question references a multi-platform game and the question or issue is unique to the SteamOS version.
SteamOS is an operating system made by Valve. It is a Linux system that was initially based on Debian and used the GNOME desktop environment, however, switched to Arch based Linux and the use of KDE Plasma 5 for the desktop environment with the release of SteamOS 3.0.
SteamOS has the Steam client installed by default. It was initially released as a beta version with the first Steam Machines on December 13, 2013. SteamOS 3.0 is also the operating system pre-installed on the Steam Deck.