Terra, or "Earth" as it is called now, is a planet.
The conditions on this planet are exactly like that in real-life Earth, so this will not be described in much detail since we all live there. What sets Terra appart from real-life Earth is mostly the organisms and the shape of the continents.
Terra orbits a star called Sol, or now known as the "Sun." Sol is a medium-sized yellow star, exactly like that of the real sun.