Power factor describes how efficiently an LED driver uses electricity. It is the ratio of the real power that is used to do work and the apparent power that is supplied to the circuit. The power factor can get values in the range from 0 to 1. The closer to 1 the power factor is, the more efficient the driver is. A good power factor is 0.9 or above.
Power factor correction refers to a system of inductors, capacitors or voltage converters that adjust the power factor of electronic devices toward the ideal power factor of 1.0.