An operating system created by Google based on the Linux kernel. Use this tag when looking for programs that need to run on Chrome OS.
Chrome OS was created by Google in 2009. It's key feature at the time was that the user data and programs were stored in the cloud - Google Drive (also owned by Google).
Chrome OS comes pre-installed on laptops called Chromebooks (ie. laptops with Chrome OS on them.)
As it developed, more programs were made for Chrome OS, and you can ask for recommendations on them using this tag.
You can learn more about Chrome OS on its Wikipedia page.