Also known as The Assumption of Mary or the Feast of the Panagia .
It is the celebration of the day that God assumed the Virgin Mary into Heaven following her death, according to popular Christian belief. It is the most important feast of the year after Easter and an occasion for big celebrations.
Panagia – which literally means “all holy” is one of the terms used for the Virgin Mary.
(Not to be confused with a panagyri, which is a local festival and can be in connection with various events, and is celebrated on different dates depending upon the local customs. Although a lot of these do take place in August. You will see that the Kissamos News calendar for August is very busy with local festivals.)
This year as the holiday is a Monday many Greeks will be treating the whole weekend as a three day holiday.
Banks and post offices will be closed. Major supermarkets will be closed on the Monday, but you may find the occasional small shop open in tourist areas. Most tavernas will be open. Petrol stations may well be closed, some also deciding to close on the Sunday. Museums which are traditionally closed on a Monday, may be open!
As usual it is difficult to be precise.
This article gives a lot more detail about the day, the customs and celebrations.