Please don't refer to "O.S." It's confusing. Why? because in this context you could be talking about :
- Open Source
- Software released along with it's source code, and a development style encouraging open development and re-use of source code. It usually implies open licensing to facilitate this development style, and it usually implies the software is 'free' as in beer and 'free' as in speech. Open Data is similar concept, particularly when it comes to licensing for re-use. All of OpenStreetMap's core software, and most of the related tools are open source.
- National mapping agency of the UK which inspired the creation of OpenStreetMap by charging too much for their map data!
- Operating System
- Low level software running on computers and devices, which enables and facilitates the running of higher level application software.
- The name of several populated places accross Norway.