MPIN stands for Mobile Banking Personal Identification Number.
It is used as a security code for online transactions.
MPIN or Mobile Pin provides an added layer of security while accessing mobile banking accounts.
MPIN number is a 4–6-digit password on mobile banking apps for authentication. Any payment through a mobile app is impossible
without entering the MPIN.
The Reserve Bank of India (RBI) has necessitated a 2-way authentication process for mobile banking transactions. It implies the provision of 2-factor identification to obtain approval.

Example:
While making payment using UPI or mobile banking a code is put to verify that the transfer is legitimate and done by the account holder. This code is called MPIn and is advised to not share with anyone