A short code is similar to a phone number, but shorter, and it can only be used for messaging.
Short codes can only be used from mobile phones. They cannot by used to place voice phone calls. Short codes are country-specific.
Short codes are typically used by companies for marketing campaigns. For example, some TV shows allow viewers to vote in polls or contests by texting specific messages to specific short codes.
Companies must rent short codes from a national short code clearinghouse that coordinates and routes short codes for the wireless carriers.