A short code is a 5 or 6 digit phone number that is used by organizations to send text messages at scale. People opt into SMS marketing programs by texting a word or phrase known as a “keyword” to a short code. They are specifically meant to be shorter than normal phone numbers to make the opt in process easier.
Additionally, SMS short codes are capable of sending extremely high volumes of text messages in a short period of time. This makes them the optimal choice when looking to reach large audiences.