In frequency-division multiplexing of telephone system channels, a grouping of supergroups, i.e., in the U.S. and Canada, a grouping of ten supergroups or 600 voice channels. Note: Some mastergroups that are used in terrestrial telephone systems consist of 300 or 900 channels that are formed by multiplexing five or fifteen supergroups, respectively. See  channel mastergroup. See also  channel,  frequency-division multiplexing,  group,  jumbo group,  multiplexing,  supergroup,  telephone system,  voice.