OTP (One-Time PIN) Code
A one-time PIN code is a code that is valid for only one login session or transaction using a mobile phone. It is often used in two factor authentication or 2FA to provide an extra layer of security for the user when he uses an ATM machine or tries to login to a service from a different computer.
Since the one-time pin is valid for only a single use, they are not vulnerable as static passwords (passwords that do not change) and cannot be reused a second time by anyone, including unauthorized persons and thus avoiding the threat of pin code theft.
There are a number of ways to deliver one-time passwords and pins with the two most common and secure ways being through proprietary tokens and mobile phones. Using mobile phones for delivering OTP's come as a logical step due to mobile phones being ubiquitous and that most of them meet hardware requirements needed to successfully deal with OTP's.
The usage of modern smartphones in delivering one-time PIN codes benefits both the end-users who are already familiar with their device and don't need to use another one and enterprises that need to deliver them, as using this method lowers their operational costs.