Looking for the meaning or definition of the word DOS? Here's what it means.
Proper noun
(computing) Acronym of Disk Operating System., especially: a collective term for disk(ette)-based operating systems (PC-DOS, MS-DOS, DR-DOS, Novell DOS, FreeDOS) available for IBM and IBM-compatible personal computers from the early 1980's, although the term was used before then to refer to any disk-based operating system (such as the Data General "Diskette Operating System" for their minicomputers, or for the TRS-80 DOS used when the computer was upgraded from cassette data storage to diskette).