From Longman Dictionary of Contemporary EnglishMS-DOSMS-DOS /ˌem es ˈdɒs $ -ˈdɑːs/ trademark one of the most common operating systems for a computerFrom Longman Business DictionaryMS-DOSMS-DOS /ˌem es ˈdɒs-ˈdɑːs/ noun [uncountable] trademark COMPUTING Microsoft Disk Operating System; one of the most common OPERATING SYSTEMs for computersMS-DOS based computer games