e-qua-tor-i-al co-ord-i-nate sys-tem
/ekwəˈtôrēəl kōˈôrdə nāt sistəm/
A celestial coordinate system widely used to specify the positions of celestial objects. It may be implemented in spherical or rectangular coordinates, both defined by an origin at the center of Earth, a fundamental plane consisting of the projection of Earth's equator onto the celestial sphere (forming the celestial equator), a primary direction towards the March equinox, and a right-handed convention.
Source: Cindy McKean, Wikipedia