A Wolter telescope is a telescope which uses reflections that are shallow, i.e., far from perpendicular to the surface, with a small angle between the surface and the beam. The design is intended for X-rays, which generally are not reflected by a surface nearer to perpendicular to the beam.
There are a number of subtypes that differ substantially other than aiming for the shallow-angle reflections. The design is common for X-ray telescopes. Examples: