The property of any communications facility, equipment, channel, or system in which the range of frequencies used for transmission is greater than 0. 1 % of the midband frequency. Note: "Wideband" has many meanings depending upon application. "Wideband" is often used to distinguish it from "narrowband,"where both terms are subjectively defined relative to the implied context. 2. In communications security systems, a bandwidth exceeding that of a nominal 4-kHz telephone channel. 3. The property of a circuit that has a bandwidth wider than normal for the type of circuit, frequency of operation, or type of modulation. 4. In telephony, the property of a circuit that has a bandwidth greater than 4 kHz. 5. Pertaining to a signal that occupies a broad frequency spectrum. Synonym broadband.