SMS, or Short Message Service, is a text messaging service that allows users to send and receive short messages on mobile devices. It typically supports messages up to 160 characters in length and is widely used for personal communication, notifications, and alerts. SMS operates over cellular networks, making it accessible even without internet connectivity. Introduced in the 1990s, SMS has become a fundamental part of mobile communication. It is often used in conjunction with other messaging platforms and applications, such as WhatsApp and iMessage, but remains popular due to its simplicity and reliability.