Wednesday is the day of the week following Tuesday and before Thursday. According to international standard ISO 8601 adopted in most western countries it is the third day of the week. In countries that use the Sunday-first convention Wednesday is defined as the fourth day of the week. It is the fourth day of the week in the Judeo-Christian calendar as well, and was defined so in the ancient Mesopotamian and biblical calendars. The name is derived from Old English Wōdnesdæg and Middle English Wednesdei, "day of Woden", ultimately a calque of dies Mercurii "day of Mercury".