A Korsch telescope is a three-mirror telescope with a wide field of view, whose design ensures that there is little stray light in the focal plane. The design has a flat image plane, meaning that images on a flat detector will be the same size at the centre as at the edges.
The most famous observatory with a Korsch telescope is the planned James Webb Space Telescope, though the design is also planned for the ESA high-resolution optical survey mission Euclid.