The Ecliptic is the plane of the Earth's orbit around the Sun. On Earth, the Sun appears to be moving in a line around the Celestial Sphere and this is the ecliptic. It 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.
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.
Celestial Coordinate System
Ecliptic Coordinate System
Kuiper Belt (K Belt)