Sep or SEP may refer to:
September (i/ˌsɛptˈɛmbər/ sep-TEM-bər) is the ninth month of the year in the Julian and Gregorian Calendars and one of four months with a length of 30 days.
September in the Northern Hemisphere is the seasonal equivalent of March in the Southern Hemisphere. In the Northern hemisphere, the beginning of the meteorological autumn is on 1 September. In the Southern hemisphere, the beginning of the meteorological spring is on 1 September.
September (from Latin septem, "seven") was originally the seventh of ten months on the oldest known Roman calendar, with March (Latin Martius) the first month of the year until perhaps as late as 153 BC. After the calendar reform that added January and February to the beginning of the year, September became the ninth month, but retained its name. It had 29 days until the Julian reform, which added a day.
September marks the beginning of the ecclesiastical year in the Eastern Orthodox Church. It is the start of the academic year in many countries, in which children go back to school after the summer break, sometimes on the first day of the month.
September 8 is the 251st day of the year (252nd in leap years) in the Gregorian calendar. There are 114 days remaining until the end of the year.