The ecliptic (or ecliptic plane) is the plane of the Earth's orbit around the Sun. From Earth, over the course of a year, the Sun appears to be moving in a line (a great circle) around the celestial sphere and the term ecliptic refers to that line around the sky, which constitutes a plane viewed from a point on it. The line can be tracked by watching which stars are behind the Sun as it sets. This line passes through the well-known list of constellations used in astrology.
The orbits of the solar system planets and many of the minor planets are not far from the ecliptic, with long-period comets less so.
A spherical coordinate system based upon the ecliptic is the ecliptic coordinate system.
In contrast, the celestial equator is the plane through Earth's equator.