NARROW BAND

Narrow Band refers to the amount of frequency that is used for a transmission.  "Narrow Band" itself implies that the transmission allowed is quite small and thus will be limited in how much voice or data information might be send using that method.

Consumer FM radio is an example of Narrow Band transmission.  Commercial FM broadcast stations are capable of transmitting voice or music at reasonable quality levels.  However, these narrow band systems would not be good for data transmission which might require much more bandwidth for better speeds.