SMS stands for Short Message Service and is a form of text messaging that is sent from one device to another. It is a text-only format that allows users to send text messages of up to 160 characters between phones. SMS is a standardized communication protocol that is used by most telephone, internet, and mobile device systems. It is a stateless communication protocol in which every SMS message is considered entirely independent of other messages. SMS is commonly used for M2M (Machine to Machine) communication, such as LED display machines controlled by SMS or vehicle tracking companies using SMS for their data transport or telemetry needs.

The main difference between SMS and MMS (Multimedia Messaging Service) is that MMS allows users to send multimedia in their messages, such as pictures, videos, audio clips, and GIFs. Additionally, MMS allows for up to 1600 characters of text in a message, which is considerably more than a standard SMS. SMS messages are limited to text only and cannot include images or videos.

In summary, SMS is a text messaging service that allows users to send text-only messages of up to 160 characters between phones. It is commonly used for M2M communication and is a standardized communication protocol used by most telephone, internet, and mobile device systems. MMS, on the other hand, allows users to send multimedia in their messages and is an enhancement to the standard SMS message.