Narrowband vs. Wideband — What's the Difference?

In radio communications, a narrowband channel is a channel in which the bandwidth of the message does not significantly exceed the channel's coherence bandwidth. In the study of wired channels, narrowband implies that the channel under consideration is sufficiently narrow that its frequency response can be considered flat.

In communications, a system is wideband when the message bandwidth significantly exceeds the coherence bandwidth of the channel. Some communication links have such a high data rate that they are forced to use a wide bandwidth; other links may have relatively low data rates, but deliberately use a wider bandwidth than "necessary" for that data rate in order to gain other advantages; see spread spectrum.

Describing communication systems with a smaller bandwidth than wideband.

Describing a communications transmission rate between that of narrowband and broadband

Responding to or operating at a wide band of frequencies;