A Shared Library is a collection of pre-compiled code that multiple programs can use simultaneously. This allows different applications to access common functions without needing to include the same code in each program, saving memory and disk space. Shared libraries are often used in operating systems like Linux and Windows to provide essential functionalities. When a program runs, it can dynamically link to a shared library, meaning it can call the library's functions as needed. This approach not only reduces redundancy but also simplifies updates; when a shared library is updated, all programs using it benefit from the improvements without needing individual modifications.