A continuous wave transmission expressed by bandwidth, or range of frequencies. Telephones turn voice vibrations into electrical vibrations of the same shape. Analog implies continuous operation in contrast with digital, which is broken up into numbers. By converting analog signals into digital, the original audio data can be preserved.
A method of transmitting signals (voice, video, data) in which the transmitted signal is analogous to the original signal. In other words, if you spoke into a microphone and saw your voice on an oscilloscope and you took the same voice as it was transmitted on the phone line and threw that signal onto the oscilloscope, the two signals would look essentially the same. The only difference would be that the electrically transmitted signal would be at a higher frequency.
A type of transmission in which a continuously variable signal encodes an infinite number of values for the information being sent (compare with "digital").