Internet, Networking, & Security Around the Web Definition of USSD Unstructured Supplementary Service Data is used for GSM communication By Priya Viswanathan Writer Former Lifewire writer Priya Viswanathan has more tan 10+ years experience writing about technology. She is an expert on tablets and mobile devices and apps. our editorial process Priya Viswanathan Updated January 06, 2020 Ezra Bailey/Taxi/Getty Images Around the Web How to Get a VPN Tweet Share Email USSD or Unstructured Supplementary Service Data is a protocol used by GSM based mobile phones to communicate with the network operator’s computer. How It's Used USSD is widely used for a variety of purposes, such as prepaid callback service, location-based content service, WAP browsing and so on. Additionally, it is also used as a part of configuring the user’s handheld on the network. Unlike the SMS, the USSD establishes a connection in real-time between the parties involved, thereby enabling a two-way communication of information as long as the connection remains open. Example An example of USSD in action would be an application on your phone that allows you to check your account balance and add more to it.