You may have heard the term USSD quite often but do you know what it means? Unstructured Supplementary Service Data or USSD is a messaging service similar to SMS which is used to send and receive messages to and from Network provider’s Computers. They are sometimes called “Quick Codes” or “Feature codes”.
When you send a SMS it is one way communication but USSD messages create real time two way communication. Therefore USSD is more responsive than SMS.
USSD can be used for services as checking the balance, activating value added services, entering for competitions, mobile banking etc.
You can read more about USSD here