Terrestrial means "Earth-like" in this context. The inner planets (Mercury, Venus, Earth and Mars) all have a stony surface, whereas the outer planets (Jupiter, Uranus and Neptune) have no real surface, but they are so-called "gas giants", that are mostly composed of more or less liquid gases. read more
Terrestrial planets also have a molten heavy metal core, few moons, and topological features such as valleys, volcanoes and craters. In our solar system, there are four terrestrial planets, which also happen to be the four closest to the sun: Mercury, Venus, Earth and Mars. read more