The general meaning of the word inclination is the angle between a reference plane and another plane or axis of direction. When it comes to astronomy, it is defined as a measure of the tilt of a certain planet’s orbital plane in relation to that of Earth.
It is a part of the six orbital parameters that describe the shape and the orientation of celestial body. Orbit is defined as a planet’s course or path. Its measurement is defined in degrees.
When you talk about the universe or the Solar System, a planet’s inclination orbit is the angle between the plane of the orbit of the planet and the ecliptic. Ecliptic is defined as the plane wherein the Earth makes its orbit.
The inclination of a planet can be measured in relation to another plane, like the Sun’s equator. Most of the planets in the Solar System have very small inclinations, in relation to each other as well as to the Sun’s equator. However, there are remarkable exceptions with these small planets, Pluto and Eris. These two planet’s inclinations to the ecliptic are roughly 17° and 44°. If you look at a very large asteroid called Pallas, its inclination is at 34°.