To ensure consistency in text communications, providers must reserve certain Keywords for universal use.
One example is the Keyword “HELP” for consumers to request assistance, so anyone can simply reply HELP to a message to get assistance regarding the messaging campaign or how they may opt-out. In addition, to make it easy for customers to unsubscribe from a campaign, other reserved words include “STOP”, “UNSUBSCRIBE” and “END”, so when a consumer replies STOP, the provider must unsubscribe the user from future communications.
These are just some of the requirements set out by the Cellular Telecommunications Industry Association or, CTIA.