An assembly of (in Britain) 300 or (in the United States) 600 voice channels on a single transmission band, formed by the combination of, respectively, five or ten supergroups each containing sixty voice channels.
Origin
1960s.
Definition of mastergroup in US English:
mastergroup
noun
Telecommunications
An assembly of (in Britain) 300 or (in the United States) 600 voice channels on a single transmission band, formed by the combination of, respectively, five or ten supergroups each containing sixty voice channels.