A transit telescope is a telescope mounted to allow rotation of its tilt between "more vertical" and "more horizontal", but cannot be otherwise aimed, i.e., no rotation through the horizontal. They are typically positioned so vertical rotation is north-south, i.e., viewing what is above the local meridian. It is intended to target stars as they pass the celestial meridian (the great circle around the celestial sphere that passes through the celestial poles and the zenith), i.e., a, undergo a meridian transit. The passage of a star across the field of view of a telescope is termed a transit.
Currently common are transit radio telescopes. Given their daytime usability, they have the opportunity to observe any target within their reach within any 24 hours, and for all-sky surveys, they can cover that whole portion of the sky with just their single degree of freedom. For very large radio telescopes, available resources can be dedicated to a larger dish rather than the mechanism to horizontally rotate it. Some large past telescopes were built that way, and more recently, some telescopes dedicated to certain all-sky investigations are built this way.