Where a device needs a username and/or password to log in, a default password is usually provided that allows the device to be accessed during its initial setup, or after resetting to factory defaults. The default username and password is usually written in the instruction manual or on the device itself.
Manufacturers of such equipment typically use a simple password, such as admin or password on all equipment they ship, in the expectation that users will change the password during configuration. Leaving such a password on devices connected to an open network (such as the internet) is a huge security risk. Some equipment, such as wireless routers, therefore ships with a randomly-generated password.
Examples of default password databases: