Mercury, Venus, Earth, and Mars are the inner planets of our solar system.

Here's why they are considered inner planets:

* Location: They orbit closer to the Sun than the outer planets (Jupiter, Saturn, Uranus, Neptune).

* Composition: They are primarily composed of rock and metal, unlike the gas giants (Jupiter, Saturn) or ice giants (Uranus, Neptune).

* Size: They are smaller and denser than the outer planets.

Let me know if you'd like to know more about any of these planets!