1) The specific frequency of the RC transmitter and receiver in RC surface and air vehicles is the channel. Within each assigned band (such as 72MHz for RC aircraft) there are several unique channel numbers, such as 72.51 or 72.89. Each RC operating in the same area must use a separate frequency channel, otherwise radio signal interference can cause erratic control. On hobby-grade RCs, the specific frequency channel is selectable by changing out cyrstals. For toy-grade RCs the specific 27MHz or 49MHz (or other) frequency channel is usually set at the factory and can't be changed. However, some RC toys come with switches for selecting from among a few of the channels for that frequency.
2) An RC vehicle has one or more controls or actions, such as for the throttle and for steering. The number of actions that the RC transmitter controls are referred to as channels. A basic 2-channel controller would have a channel for throttle and another for turning left and right. A typical 4-channel RC airplane controller might have controls for throttle, diving/climbing (elevator), turning left and right (rudder), and rolling left and right (aileron). Other channels on transmitters are for controlling additional features including lights and sounds.
