Linked from
The 11 pages that link to Power factor, each with the reason it gives.
Alternating currentRelated: Phase shifts can make AC supply current deliver less useful real power.
Electrical powerRelated: It shows how much apparent power becomes useful net energy transfer.
Reactive powerRelated: Reactive power lowers power factor when real power remains unchanged.
AC powerRelated: It measures how effectively apparent power becomes useful real power.