The document discusses the tilt of the Earth's axis and how it causes seasons. The Earth's axis is tilted at 23.5 degrees from the plane of its orbit around the Sun. This tilt is called the inclination of the Earth's axis. It is the inclination that results in different parts of Earth receiving more or less sunlight over the course of a year, causing the seasons. The document encourages watching a video to better understand how the Earth orbits and rotates around the Sun along a fixed path, and how the tilted axis affects the seasons.