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://www.adobe.com/supportservice/devrelations/typeforum/glossary.ht