1. The sun's apparent circular path through the heavens or over the celestial sphere in the course of a year.
2. The path, against the background of stars, that the sun appears to follow each year as it is orbited by the earth.

It can be thought of as the plane of the earth's orbit projected on to the celestial sphere or imaginary sphere around the earth.

The ecliptic is tilted at about 23.5° with respect to the celestial equator, a result of the tilt of the earth's axis relative to the plane of its orbit around the sun.