A Dynamic Link Library (DLL) is a file format used in Microsoft Windows that contains code and data that multiple programs can use simultaneously. This allows for efficient memory usage and modular programming, as developers can create reusable components that different applications can share. When a program needs a specific function, it can call the DLL instead of having that code embedded within its own files. DLLs help reduce the size of applications and make updates easier. When a DLL is updated, all programs that use it benefit from the improvements without needing to be recompiled. This system promotes better organization and maintenance of software, enhancing overall performance and user experience.