A sight is a aiming device used to assist in aiming a long-range weapon, measuring instrument, or optical lighting device at a target. The sighting device can be a set of simple marking or marking system, which must be aligned with the target (such as the iron sighting device on the gun), or optical equipment, so that the user can see the sometimes optically enhanced (for example, magnified) image alignment point (such as telescope sight, reflector sight and holographic sight) aiming at the target. There are also sights that project aiming points (or "hot spots") onto the target itself, such as laser sights and infrared illuminators on some night vision devices.

In short, the sight is usually composed of two parts, the front sight and the rear sight must be aligned. Such attractions can be found on many types of equipment, including weapons, measuring instruments and navigation tools.

In weapons, these collimators are usually made of solid metal parts, so they are named "iron collimators", which are different from optical or computer collimators. On many types of weapons, they are built-in and can be fixed, adjusted or marked with elevation, wind resistance, target speed, etc. They are also classified in the form of notches (open holes) or apertures (closed holes). These types of sight may require a lot of experience and skill, because the user must maintain the correct eye position and focus on the rearview mirror, front sight and target at the same time, and all must be kept at different distances, and aim at all three focus planes.