An Equatorial Mount is a telescope mount including an axis parallel to Earth's so by rotation around that axis, the telescope can maintain its target in view.
The alternative mount is the Altazimuth Mount which requires coordinated rotation around two axes to keep its target in view.
Equatorial mounts require extra engineering that makes it inefficient to use them for the the largest telescopes, which use computer control to provide the necessary coordination to keep the telescope on target. A large telescope with an equatorial mount is the Hale Telescope at Mount Palomar Observatory.
Anglo-Australian Telescope (AAT)