What is the meaning of 1x in vibration analysis?

Consider a pump is running at 3000 RPM i.e. 50 revolutions per second or 50 Hz. If the impeller of the pump is having static imbalance, the pump generates the vibration at 50Hz. Since the frequency of vibration is the same as the RPM of the pump, the frequency of vibration is expressed as 1 \times RPM. Similarly, if the pump is having radial misalignment with the motor, the pump will vibrate at 100 Hz frequency. Hence its frequency of vibration is 2 \timesRPM. It is very meaningful to represent the vibration of a fault in terms of RPM. 1\times represents the frequency of vibration of equipment (due to fault) in terms of its RPM.