How Secure Is A Password?

New technologies and more powerful computer systems have made it important in the last years to create secure passwords to avoid successful automatic password cracking attempts via brute force and dictionary attacks. But how do passwords have to look like to be considered secure? And who determines that? There is no authority with guidelines on the creation of secure passwords. Companies, organizations, software developers and end users all have their own definition of secure passwords.
How Secure Is A Password?