Cybertron is the home planet of Cybertronians. Unlike the Earth, which is only organic, Cyberton is fusion of organic life and mechanical one.  Primus, the creator of Cybertronian race, lives in the core and the whole planet is his body. Because of the war, the planet was destroyed and didn't allow the existence of life. Now when Cybertron has been restored, Cybertronians returned to their home.