Short codes are shorter than traditional long numbers, and they're typically between five and six digits in length. Short codes are country-specific, so they must be set up on the mobile network operators to ensure full coverage within a country.
Dedicated short code is unique to your organization. The short code is set up specifically for your company. A shared short code is one that is shared amongst multiple organizations, and is differentiated between companies using unique 'keywords'.
Organizations may opt to have a 'unique company short code' which is shared among multiple campaigns. The keyword which is sent at the start of the text identifies which campaign the message belongs to and is distributed accordingly over the SMS API.
For example, customers could be asked to send 'info' at the start of their message. STOP and opt-out messages can be included.
This method is quite similar to how shared text messaging works with email marketing campaigns where you can segment your list into different groups depending on keywords in each email segmentation field that are sent at the beginning of each message (e.g., [first name], [last name], etc.).