Droids are mechanised bodies designed for specific purposes. Usually they have limited sentience, which is largely considered to be the difference between droids and robots. Some of them resemble humans while most don't. They are built and used by many civilisations throughout the Milky Way Galaxy and beyond, including The Imperium and the Rebel Alliance.
Droids usually have a specific task set to them as they are designed by purpose, such as cleaning droids[Tales 1].