Analog signal: The value of a signal (voltage , current , or frequency) that changes continuously with time and can have any meaning at any moment is called analog signal. This is often called continuous time signal . A perfect example of an analog signal is the sequence that produces variable electrical signals by converting various physical quantities found in nature, such as temperature , pressure, etc., into equivalent electrical signals. Analog circuits such as filters , amplifiers , modulators, etc. are used to process such signals. References : Bissoy.com