Although I loved Agatha Christie's books I never considered them a genre of their own. They were simply mysteries in a cozy setting. Writing World describes cozy mysteries as a bloodless crime, Cozy-Mystery.Com notes that the protagonist is usually a woman amateur sleuth, Nathan Bransford describes a cozy as a book you would want to curl up with on a cold rainy afternoon, others compare them to the Murder She Wrote series.
But cozies, in my opinion, are described by what is missing from a mystery/thriller:
There are no gruesome details
An animal or pet never, never, never gets hurt or killed
The protagonist/sleuth is rarely in danger
The profession of the sleuth is not in law enforcement
The setting is not a large city (those are hard boiled mysteries) but in an enclosed area - a village, or house
If you love cozies, hop on over to CozyMystery.Com where there is a wealth of information