reticle

A reticle, or reticule (from Latin reticulum, meaning "net"), also known as a graticule (from Latin craticula, meaning "gridiron"), 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. Today, engraved lines or embedded fibers may be replaced by a computer-generated image superimposed on a screen or eyepiece. Both terms may be used to describe any set of lines used for optical measurement, but in modern use reticle is most commonly used for gunsights and such, while graticule is more widely used for the covers of oscilloscopes and similar roles.