Low Mass, also known as “missa lecta,” or “read Mass,” is just what the name suggests–it is done without much ceremony, only read, no singing. Usually there will be one or two servers, but no more.
Sung Mass, as the name suggests, is a Mass that is sung. There will be incense, about five or six servers, and a choir or at least a cantor.
And over all of these is the “High Mass” or “Solemn Mass,” which has several servers, and a subdeacon and deacon serving alongside the priest, and thus much more ceremony.
-Fr ACEGC