Editing Signal (section)

==Definitions==
Definitions specific to sub-fields are common: 
* In [[electronics]] and [[telecommunications]], ''signal'' refers to any time-varying [[voltage]], [[electric current|current]], or [[electromagnetic wave]] that carries information.
* In [[signal processing]], signals are analog and digital representations of analog physical quantities. 
* In [[information theory]], a signal is a codified message, that is, the sequence of [[state variable|states]] in a [[communication channel]] that encodes a message. 
* In a communication system, a ''transmitter'' encodes a ''message'' to create a signal, which is carried to a ''receiver'' by the communication channel.  For example, the words "[[Mary had a little lamb]]" might be the message spoken into a [[telephone]]. The telephone transmitter converts the sounds into an electrical signal. The signal is transmitted to the receiving telephone by wires; at the receiver it is reconverted into sounds.
* In telephone networks, [[Signaling (telecommunications)|signaling]], for example [[common-channel signaling]], refers to phone number and other digital control information rather than the actual voice signal.