Symbian OS is a mobile operating system designed for smartphones, originally developed by Symbian Ltd. in the late 1990s. It was widely used by various manufacturers, including Nokia, and became popular for its multitasking capabilities and support for third-party applications. The operating system is known for its efficient use of resources, making it suitable for devices with limited hardware. Although it dominated the smartphone market for several years, its popularity declined with the rise of other platforms like iOS and Android, leading to its eventual discontinuation in 2014.