Iron Sights
Non-optical sights — a front sight and a rear sight aligned by eye.
Iron sights are the original aiming system: a front sight (post or bead) and a rear sight (notch or aperture). Even with a red dot or scope mounted, backup iron sights (BUIS) are wise — optics fail. Three-dot sights, fiber-optic, and tritium night sights are common modern variants.