AccountManager keeps track of cloud login information on Android devices. It uses plugins to communicate with different kinds of services, and the user only has to enter the information once. Applications don't need to deal with passwords, and may instead ask for permission to gain access to specific accounts.
As a part of Google's Android SDK, the AccountManager can be used create a separation of the cloud account information entered by the user and the applications that make use of it. Since web services are constructed differently from each other, AccountManager uses plugins (authenticators) in order to communicate with them.
An application can ask for permission to access a certain account. If successful, the application receives a token, and never has to deal with the actual password. The user can find a list of all accounts that are used on the device under Settings > Accounts & sync, and may at any time remove an account that shouldn't be accessed anymore.
