Analog is an adjective that describes a device or system in which information is represented by continuously variable physical quantities. A record player is a simple example of an analog device; the needle continuously reads the bumps and grooves on a record. A clock with hands is also an example because the hands move continuously around the face and the clock is capable of indicating every possible time of day.
Analog contrasts with digital. While a record player is analog, a CD player is digital since it reads binary data that represents an audio signal. While a clock with hands is analog, a clock that is digital can only represent a finite number of times, such as every tenth of a second. Generally, computers are digital devices while the human experience is analog. For example, our vision and hearing is a continuous transmission of information to our senses. There are infinitely smooth gradations of shapes, colors, and sounds.
Analog signal vs. digital signal
An analog signal is a continuous signal in which one time-varying feature, such as pressure or voltage, represents another time-based variable. One variable is the analog of another. Analog signals allow for an infinite number of values to be represented, for example, a light dimmer. A digital signal expresses variation in response to a set of distinct values, for example, a light switch that can only be turned on or off, not dimmed.
Analog signals are mostly used to describe electrical signals such as audio recording and reproduction, live amplification devices, radio signals, and older video signal transmission technologies such as VGA. While analog versions have mostly been replaced by their digital counterparts, it still exists in the form of AM/FM radio and home recordings on audio cassettes or VHS tapes.
Analog signals are best suited for audio and video transmissions, have much higher density to present more refined information, use much less bandwidth than digital sounds, and preserve the natural form of a sound. In contrast, digital signals are easy to compress, edit without altering the original copy, transmit the data over networks, and can be encrypted.