From Longman Dictionary of Contemporary Englishoperating systemˈoperating ˌsystem noun [countable] TDa system in a computer that helps all the programs in it to work together
Examples from the Corpus
operating system• The toolset will include a layer that implements Windows APIs on the System 7 operating system.• We like fast computers, the latest operating system, neat software and expensive peripherals as much as anyone.• None of the top 10 clonemakers now sells computers that run the Macintosh operating system.• The new mainframe operating system I have personally approved is going haywire; the computer is down half the time.• Later in the year, a multiprocessing operating system derived from Unisys' current product will appear.From Longman Business Dictionaryoperating systemˈoperating ˌsystem [countable]COMPUTING the most basic software on a computer that allows it to work and programs to work on itWindows is easily the dominant operating system of its kind in the desktop computer market. → system 