Unsubscribe

Unsubscribe refers to the process of a customer removing themselves from a database in order to not be contacted again. With SMS this is done automatically when a customer texts an unsubscribe keyword into a Dedicated Reply Number or SMS Shortcode.

Businesses or individuals will need to instruct the recipient how to unsubscribe from their campaigns in order for them to automatically remove themselves from receiving future text messages.
e.g. Reply STOP to unsubscribe from future campaigns

References

Wikipedia