The Death Star was the code name of unspeakably powerful and horrific weapons developed by the Empire. The first Death Star was an immense space station that carried a weapon capable of destroying entire planets. The Death Star was to be an instrument of terror, meant to force rebel worlds into surrender under the threat of destruction.
While the massive station is evidence of the evil nature of the Empire, it was also proof of the Empire's greatest weakness -- the belief that technology and terror were superior to the will of beings fighting for freedom. The Rebel Alliance was able to defeat the Death Star threat, as well as a second battle station constructed after the first's destruction.