The Kuiper belt is a region just past Neptune which forms a ring round our solar system. This area is believed to be the location from which comets and other objects or TNO's (Trans-Neptunian objects) come from. The belt is located about 30-50 AU away and as I have already mentioned is just past where Neptune lies, thus Trans-Neptunian.  In the Kuiper belt are many objects that don't exceed over 100 km but also 10,000 or more which exceed that size. This gives the belt a wide variety of sized objects. Most of the objects in the Kuiper belt are believed to be made of ice, composed of "light hydrocarbons, ammonia, and water ice"  but with a wide variety of colors the surface of most of the objects is identified as anything from "dirty ice to hydrocarbons."  The objects in the Kuiper belt are the remnants of the formation of the solar system. It is thought that what is in the Kuiper belt is what wasn't swept up by the outer planets.

https://www.space.com/16144-kuiper-belt-objects.html
https://www.universetoday.com/107598/what-is-the-kuiper-belt