KPIs are metrics that are: tied to an business goal; have at least one defined time-sensitive target value; and have explicit thresholds which grade the gap between the actual value and the target. Distinguished from other metrics, key performance indicators (KPIs) are those metrics most critical to gauging progress toward business goals.

Key outcome indicator (KOI): Often used in the public sector to describe key performance indicators.

Taken from http://www.pilotsoftware.com/resources/pm_glossary.html