What is meant by Overall Vibration?
Vibration is the to and fro motion of an object from it's mean position of rest. Motion of a Pendulum is an example of Vibration. Motion of a swing at a Park is an example of Vibration. Similarly, plant machines like Motors, Pumps, Fans and more exhibit Vibration. This vibration is usually small and not visible sometimes to the naked eye. Thus, special tools like Vibration Meters are used to measure vibration.
The Amplitude of Vibration (either in Acceleration or Velocity or Displacement) measured by a Vibration Meter is called as Overall Vibration
Why the term 'Overall'? Because Vibration Meters do not measure vibration at a single frequency. Vibration meters consider all possible frequencies of vibration within their minimum and maximum frequency windows (Fmin and Fmax respectively) and provide the net value of vibration.
Vibrations at different frequencies with different amplitudes superimpose to create the net vibration - which is the overall vibration