Shared Long-Code is the common number for a group of people. For MSG91 the shared Long-Code is 9229224424/6262642222. Using this number will be free of cost, you will be charged only for the incoming SMS. Incoming SMS is differentiated by keyword, and hence your keyword must be unique.
Dedicated Long -Code will be 10 digits mobile number of your choice. There will be a one-time set-up cost for the new mobile number. The keyword can be of your choice as the incoming SMS are differentiated by the mobile number in this case.