Power Factor is a measure of how efficiently electrical power is consumed.
The ideal Power Factor is unity - or one. Anything less than one, (or 100% efficiency), means that extra power is required to achieve the actual task at hand.

Power Factor Correction is the term given to a technology that has been used since the turn of the 20th century to restore Power Factor to as close to unity as is economically possible.

This is normally achieved by the addition of capacitors to the electrical network, which compensate for the Reactive Power demand of the inductive load and thus reduce the burden on the supply.