SMS stands for Short Message Service, which is a text messaging service component of most telephone, internet, and mobile device systems. It uses standardized communication protocols that allow mobile devices to exchange short text messages of up to 160 characters between phones. SMS is the most common form of text messaging used today.

SMS messages are text-only messages without an attached file, like a picture, video, emoji, or a website link. They are used for a variety of purposes, including personal communication, mobile marketing, and machine-to-machine communication. SMS messages are generally treated as lower-priority traffic than voice, and various studies have shown that around 1% to 5% of messages are lost entirely, even during normal operation conditions, and others may not be delivered until later.

In contrast, MMS stands for Multimedia Messaging Service, and it refers to messages with a picture or video. A text message of up to 160 characters without an attached file is known as an SMS, while a text that includes a file becomes an MMS.