Greek yogurt is a yogurt that has been strained to remove
most of its whey, resulting in a thicker consistency than unstrained
yogurt, while preserving yogurt's distinctive sour taste. Like many types
of yogurt, strained yogurt is often made from milk that has been enriched
by boiling off some of its water content, or by adding extra butterfat and
powdered milk. In Europe and North America, it is often made with low-fat
or fat-free yogurt. In Iceland a similar product named skyr is produced.
Read on Wikipedia