A rocky terrestrial planet is a planet that is composed of silicate rocks or metals. One important characteristic of this type of planets is that they have a solid planetary surface. This is significantly different from planets such as the larger giant planets (which are composed of a combination of hydrogen, helium and water).
A rocky terrestrial planet that is twice as large as the Earth but at the same distance of its star would have several geological characteristics. It would most likely have a central core made out of a metal, most likely iron. It would most likely have a complex topography, and we would be able to see craters, volcanoes, mountains or canyons on its surface.