daysOfWeek

Days of the week, often referred to through the term daysOfWeek, are a standard sequence of seven temporal units used in most calendars to organize time. The commonly used English names are Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, and Sunday, with abbreviations Mon, Tue, Wed, Thu, Fri, Sat, Sun. In many languages, the names reflect historical and cultural influences, including references to celestial bodies and deities.

International standards and local practice differ in the starting point of the week. ISO 8601 designates Monday as day 1 and Sunday as day 7, a convention widely adopted in Europe and international contexts. Other locales treat Sunday as the first day of the week. In computing and data formats, daysOfWeek is often represented as an indexed list or enumeration, with varying conventions: some systems index 0–6 starting with Sunday, others use 1–7 starting with Monday.

Usage and terminology distinguish weekdays from weekends and business days. Weekdays typically refer to Monday through Friday, while weekends cover Saturday and Sunday in many places; some regions observe Friday and Saturday as the weekend. Holidays and local customs can affect scheduling and the length of the working week. Calendar applications, scheduling systems, and date-time libraries rely on daysOfWeek to enable parsing, formatting, and calculations of dates, durations, and recurrences.

Historically, day names derive from Latin and older Germanic traditions. Latin dies Lunae, dies Martis, and the like influenced early naming, while English and other languages adapted these roots through Germanic and Norse linguistic layers to form the modern daysOfWeek.