(, also anglicized as Deen) is a Persian  word which is commonly associated with Zoroastrianism and Islam, but it is also used in Sikhism and Arab Christian worship. The term is loosely associated with "religion", but as used in the Qur'an, it means the way of life in which righteous Muslims are obligated to adopt in order to comply with divine law (Quran and sunnah), or Shari'a, and to the divine judgment or recompense to which all humanity must inevitably face without intercessors before God. Thus, although secular Muslims would say that their practical interpretation of Din conforms to "religion" in the restricted sense of something that can be carried out in separation from other areas of life, both mainstream and reformist Muslim writers take the word to mean an all-encompassing way of life carried out under the auspices of God's divine purpose as expressed in the Qur'an and hadith. As one notably progressive Muslim writer puts it, far from being a discrete aspect of life carried out in the mosque, "Islam is Din, a complete way of life".

DIN or Din or din can have several meanings:

• Din, an Arabic term meaning "religion" or "way of life"
• Din (Kabbalah), one of the ten aspects of the Ein Sof in Kabbalah (more commonly known as "Gevurah")
• Din (surname)
• DIN is the abbreviated name of the Deutsches Institut für Normung (German Institute for Standardization) and is used in the names of its standards, like:
  • DIN 1451, German Standard Committee chosen typeface from 1936.
  • DIN 4512, a definition of film speed
  • DIN 476, as for example DIN A4, is a scale for paper sizes.
  • DIN 31635, an Arabic transliteration scheme.
  • DIN 72552 is a standard for automobile electric terminal numbers.
  • DIN connector, one of a number of electrical (audio/video/keyboard) connectors following DIN standards.
  • DIN fitting, a type of high-pressure air or gas connection used in some modern very high-pressure scuba gear.
  • DIN ISO 7736, size standard for car audio head units.
  • DIN Panel cutout size, a standard for cutouts for industrial panel mount equipment.
  • DIN rail, a common system for mounting circuit breakers and industrial control equipment inside equipment racks.
  • DIN ski binding scale, scale to ensure ski bindings release under the same force at all skiing destinations worldwide.
  • FF DIN, 1995 digital typeface
• Din, Guinea
• Din, Iran
• Drug Identification Number - a unique number given to all drugs sold in Canada.
• Din (The Legend of Zelda), a goddess in The Legend of Zelda series of video games
• Serbian dinar, a local abbreviation

(DIN; in English, the German Institute for Standardization) is the German national organization for standardization and is the German ISO member body. DIN is a Registered German Association (e.V.) headquartered in Berlin. There are currently around thirty thousand DIN Standards, covering nearly every field of technology.