Wednesday is the day of the week between Tuesday and Thursday. According to international standard ISO 8601, it is the third day of the week. In countries which have Friday as their holiday, Wednesday is the fifth day of the week. In countries which use the Sunday-first convention, and in both the Islamic and Jewish calendars, Wednesday is the fourth day of the week.

In many languages, the names given to the seven days of the week are derived from the names of the classical planets in Hellenistic astronomy, which were in turn named after contemporary deities, a system introduced by the Sumerians and later adopted by the Babylonians from whom the Roman Empire adopted the system during late antiquity. In some other languages, the days are named after corresponding deities of the regional culture, beginning either with Sunday or with Monday. The seven-day week was adopted in early Christianity from the Hebrew calendar, and gradually replaced the Roman internundinum.