Source : Free On-Line Dictionary of Computing

Write-Once Read-Many
     
         (WORM) Any type of storage medium to which data can
        be written to only a single time, but can be read from any
        number of times.  Typically this is an {optical disk} whose
        surface is permanently etched using a laser in order to record
        information.  WORM media have a significantly longer shelf
        life than magnetic media and thus are used when data must be
        preserved for a long time.
     
        (1996-04-01)