'Modulation'
Modulation is the process of varying a periodic waveform in order to use that signal to convey a message. A device that performs modulation is known as a modulator, one that preforms the inverse is called a demodulator. A device that does both is called a modem.
Amplitude Modulation
It is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. A modulated signal y(t) can be understood as the product of two signals, the information bearing signal x(t) and the carrier signal c(t). Generally c(t) is either a complex exponential or a sinusoidal function.
Both the complex exponential and sinusoidal function have a certain carrier frequency Wc associated with it. For the signal to be successfully demodulated the carrier frequency should be less than the maximum frequency of the modulating signal.
