October is the tenth month of the year in the Julian and Gregorian Calendars and one of seven months with a length of 31 days. The eighth month in the old Roman calendar, October retained its name (from the Latin "octo" meaning "eight") after July and August, named after Julius and Augustus Caesar respectively, were inserted into the calendar that had originally been created by the Romans.

October is commonly associated with the season of autumn in the Northern hemisphere and spring in the Southern hemisphere, where it is the seasonal equivalent to April in the Northern hemisphere.

In common years January starts on the same day of the week as October, but no other month starts on the same day of the week as October in leap years. October ends on the same day of the week as February every year and January in common years only. In leap years, October starts on the same day as August of the previous year.