USSD stands for Unstructured Supplementary Service Data. It is a communications protocol used by GSM cellular telephones to communicate with the mobile network operator's computers

. USSD can be used for various purposes such as WAP browsing, prepaid callback service, mobile-money services, location-based content services, menu-based information services, and as part of configuring the phone on the network

. Unlike SMS, USSD messages create a real-time connection during a USSD session, allowing a two-way exchange of a sequence of data, making it faster than SMS

. USSD messages are up to 182 alphanumeric characters long, and the service does not require a messaging app, nor does it incur charges

. It is commonly used by prepaid GSM cellular phones to query the available balance, refill the balance on the user's SIM card, and to deliver one-time passwords or PIN codes