Power factor
The fraction of apparent power (V × I) doing real work: PF = P/|S| = cos φ for sinusoids. At PF 0.7, the wires carry ~43% more current than the useful power requires — the extra just sloshes back and forth.
In practice
Utilities bill industry for poor PF because their wires and transformers are sized by current, not work. Correction means adding the opposite reactance — typically capacitors across inductive (motor) loads — sized for the actual operating point.