UPI stands for Unified Payments Interface. It is a system that brings together multiple bank accounts (of participating banks) into a single mobile application, merging different banking features and merchant payments under a single roof. To explain in lucid language, if you have bank accounts in different banks registered with the same phone number, you can access all of your accounts through a single app. The app brings all your bank accounts under a single UPI ID through which you can transfer money, pay to merchants, and access several other banking facilities. It is entirely a mobile-based interface, wherein, most transactions happen on the mobile through a unique ID known as VPA (Virtual Payment Address). Bank account details, account number, IFSC codes, etc. are not required in UPI transactions.