The apparent path of the Sun across the sky over the course of a year, representing the plane of Earth's orbit projected onto the celestial sphere. The zodiac constellations lie along this path.
From Greek 'ekleiptikos' meaning 'of an eclipse,' because eclipses can only occur when the Moon crosses this plane. Ancient astronomers noticed that eclipses happened only when celestial bodies aligned along this specific path across the sky.
The ecliptic is tilted 23.5 degrees relative to Earth's equator, and this tilt is what gives us seasons! If Earth's axis weren't tilted, we'd have no seasons and the ecliptic would coincide with the celestial equator.
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