Any representation of a physical quantity (e.g. displacement) in terms of a continuous variation of a second physical quantity (e.g. voltage) is known as analogue representation. Most measurement devices (e.g. accelerometers, strain gauges, thermocouples and microphones) generate analogue signals.
Quantities in two separate physical systems having consistently similar relationships to each other are called analogous. One is then called the analogue of the other. The electrical output of a transducer is an analog of the vibration input of the transducer as long as the transducer is not operated in the nonlinear (overloaded) range.
This is in contrast to a digital representation of the vibration signal, which is a sampled and quantised signal consisting of a series of numbers, usually in binary notation.