A reticle (or reticule) is a net of fine lines or fibers in the eyepiece of a sighting device, such as a telescope, a telescopic sight, a microscope, or the screen of an oscilloscope. The word reticle comes from the Latin "reticulum," meaning "net." Today, engraved lines or embedded fibers may be replaced by a computer-generated image superimposed on a screen or eyepiece. The term graticule is the synonymous term from French, coming from the Latin craticula for gridiron. Both may be used to describe any set of lines used for optical measurement, but in modern use the term reticle is most commonly used for gunsights and such, while graticule is more widely used for the covers of oscilloscopes and similar roles.
There are many variations of reticles; this article concerns itself mainly with a simple reticle: crosshairs. Crosshairs are most commonly represented as intersecting lines in the shape of a cross, "+", though many variations exist, including dots, posts, circles, scales, chevrons, or a combination of these. Most commonly associated with telescopic sights for aiming firearms, crosshairs are also common in optical instruments used for astronomy and surveying, and are also popular in graphical user interfaces as a precision pointer. The reticle is said to have been invented by Robert Hooke, and dates to the 17th century.