Wikipedia
In Armenian Christian tradition, matagh ( mataġ) is a lamb or a rooster slated for sacrifice to God, a ritual which has continued from the pagan past. In many regions of Armenia today, this pagan-Christian synthesis is very much alive in the regular slaughter of chosen animals in front of churches. Matagh is done often to ask God for either forgiveness, health, or to give them something in return. People generally gather at the house where the Matagh was done, where they pray and eat the meat. Tradition holds that the meat must be eaten before sundown.
Additional information: The meat is to be prepared in a simple way stove top (usually Khashlama) with minimal spices. It is not to be grilled over a fire. Also the meat is supposed to be shared among 7 families (relatives and/or neighbors). Frequently a Matagh takes place as a thank you to the gods after an accident or other life-threatening event with a good outcome.