Period
The period of a repetitive signal, such as a sine wave, is the length of time between one point in the cycle to the same point on the next cycle and is the inverse of the frequency.

Phase
Phase is the measure of the angular relationship, measured in degrees between two events. In the context of balancing it is the relationship between the sine wave generated of the out-of-balance forces compared with a one-per-revolution time reference signal.

Peak-Peak
The amplitude of a sine wave measured from the maximum positive to the maximum negative.

Peak
The amplitude of a sine wave measured from neutral or zero to the maximum positive or maximum negative value.

Piezoelectric Effect
Originates from the Greek piezein to ‘press or squeeze’. When certain types of man-made or naturally occurring crystalline structures are deformed by the application of a mechanical force they generate an electrical signal.