The Free On-line Dictionary of Computing (30 December 2018):

Multiple Master

    (Or "Multiple Master Font") A font
   that is a mixture of two or more other fonts.

   A Multiple Master font is a single font containing from two to
   sixteen master designs (the current implementation limit).  A
   weight factor specifies the contribution of each master design
   for the creation of a multiple master font instance.

   A Multiple Master instance is a single interpolation of a
   multiple master font as created by a user or application.

   ATM Glossary

(http://adobe.com/supportservice/devrelations/typeforum/glossary.html).

   Useable fonts

(http://susi.informatik.rwth-aachen.de/Mirror/winsite/win3/fonts_atm.html).

   (1998-05-31)