An SMS, or Short Message Service, is a text messaging service that enables the exchange of short text messages between mobile devices. Typically, an SMS message is limited to 160 characters and is transmitted over cellular networks using standardized communication protocols

. SMS was developed as part of the GSM standards and launched in the early 1990s, originally intended for simple alerts from carriers. It has since become the most widely used form of text communication globally, supporting personal, business, and commercial uses such as marketing, two-factor authentication, and mobile banking

. The way SMS works involves the sender's device transmitting the message to a centralized Short Message Service Center (SMSC), which routes and stores the message until the recipient's device is available to receive it. The message is then delivered to the recipient's device, which may send a delivery confirmation back to the sender's SMSC

. SMS is text-only and does not natively support multimedia content like pictures or videos; for that, Multimedia Messaging Service (MMS) was developed as an extension. SMS messages are very reliable and can be sent even in areas with limited network coverage or during congestion because they use signaling channels rather than voice or data channels

. In summary, SMS is a fundamental, standardized service for sending brief text messages between mobile devices, widely used worldwide for both personal and commercial communication.