Green Tritium Outline Orange Square (non trit) REAR for Glock Gen 1-4 Green Tritium Outline: Tritium is a radioactive isotope of hydrogen commonly used in firearm night sights. It emits a glow in low-light conditions, aiding in target acquisition. The "green" likely refers to the color of the illumination provided by the tritium. Orange Square (non Trit) Rear: This suggests that the rear sight has a non-tritium element, possibly an orange square, which may not glow in the dark. Non-tritium elements are often used for daytime visibility. For Glock Gen 1-4: This indicates that these sights are designed to fit Glock handguns from the first to the fourth generations. In summary, the description seems to refer to a set of handgun sights designed for Glock Gen 1-4 pistols. The rear sight has a green tritium outline for low-light conditions, and there's a non-tritium orange square for daytime visibility. Such sights are commonly used to provide shooters with a reliable aiming solution in various lighting conditions.