A passcode is a numeric sequence used to authenticate a user on computer or electronic device. The term is sometimes used synonymously with "password," but technically a passcode only contains numbers.
The security of a numeric passcode is proportional to how many digits it contains. Since there are ten possible values for each digit (0-9), the number of possible codes is equal to ten times the number of digits. For example, a four-digit passcode can have 104 or 10,000 different combinations. A six-digit passcode can have 1,000,000 different combinations.
Passcodes provide quick and easy authentication and are commonly used on devices that have a numeric keypad interface, such as ATMs, electronic safes, and security system control panels. In the case of ATMs and other systems that require a personal identification number (PIN), your PIN may double as your passcode.
Since passcodes only contain integers, they are naturally less secure than passwords or passphrases. Therefore, devices that provide passcode authentication often disallow access after a certain number of failed login attempts. For example, if you passcode-protect your smartphone and enter the wrong passcode multiple times, you may be required to wait several minutes before you can attempt to log in again.
Updated: October 14, 2015