An SMS short code is a 5-6 digit number that is used to opt-in consumers, and then used to send text message competitions, promotions, etc. A consumer interacts with an SMS short code by sending a new text message from their mobile device, expressing interest in the promotion.

Use 5 digit short codes for powerful SMS marketing campaigns, lead generation, competitions or information drives. Shortcodes are easy to remember and a sure-fire way to amplify your other marketing initiatives.

Short codes, or short numbers, are short digit sequences, significantly shorter than telephone numbers, that are used to address messages in the Multimedia Messaging System (MMS) and short message service (SMS) systems of mobile network operators. In addition to messaging, they may be used in abbreviated dialing.

Short codes are designed to be easier to read and remember than telephone numbers. Short codes are unique to each operator at the technological level. Even so, providers generally have agreements to avoid overlaps. In some countries, such as the United States, some classes of numbers are inter-operator (U.S. inter-operator numbers are called common short codes).

Read more by visiting Wikipedia - https://en.wikipedia.org/wiki/Short_code