All Saints’ Day(Solemnity of All Saints,All Hallows, Hallowmas or All Saints)is celebrated on 1 November by most Western Christians and is to honor all saints known and unknown. In some Catholic countries, it is a holiday. It is a holy day of obligation for most Catholics except when it falls on a Saturday or Monday. In that case it is celebrated on Sunday. Eastern Orthodox is celebrated on the first Sunday after Pentecost and is called All Saints’ Sunday.

All Saints Day (About.com)