The power factor is the phase angle between voltage and current (cosφ).
cos phi (φ) is used (among other purposes) to calculate the power consumption of a motor.
Power consumption is indeed of high importance when it comes to pumps. For pumps with standard AC motors, the power input is found by measuring the input voltage and input current and by reading the value cosφ at full load on the motor name plate. Cosφ is the phase angle between voltage and current. Cosφ is also referred to as power factor (PF). The power consumption P1 can be calculated by the formulas shown below depending on whether the motor is a single-phase or a three-phase motor.
AC single-phase motor, e.g. 1 x 230 V
P1 = U x I x cosφ
AC three-phase motor, e.g. 3 x 400 V
P1 = √3 x U x I X cosφ