OS X Mountain Lion: Understand passwords
OS X is designed to give you a safe and secure computing environment. The security of your computer depends a great deal on using secure passwords in key areas of the system.
A login password, also called an user password, is used in the login window and allows the user access to their Mac. Their privileges are limited by the type of user they are. An administrator user is required to perform many important tasks, such as setting certain system preferences, installing software, and administering standard users.
Passwords in Keychain Access
The Keychain Access utility stores passwords for various apps and services. Keychain Access can remember these passwords and save you the effort of authenticating separately for each of the items on your keychain. The keychain is secured by a keychain password which is unlocked when a user logs in.
When FileVault is use to encrypt a disk, a recovery key is created as a safeguard to unlock the encoded contents of the disk if users forget their login passwords. The recovery key should not be physically stored with the computer where it can be discovered. You can also have Apple store your Recovery key.