Discreet Frequency
From the General Planning Handbook
DISCRETE FREQUENCY
A separate radio frequency for use in direct pilot-controller communications in Air Traffic Control which reduces frequency congestion by controlling the number of aircraft operating on a particular frequency at one time. Discrete frequencies are normally designated for each control sector in enroute/terminal Air Traffic Control facilities. Discrete frequencies are listed in the Airport/Facility Directory, and DoD FLIP IFR Enroute Supplement.