DLL stands for Dynamic Link Library. A DLL is an application extension, loaded and unloaded automatically by an application during its execution. The advantages of DLLs are that they can be unloaded during application execution and return at that time their memory to the operating system and that one instance of the DLL can be shared by one or more applications, again reducing memory requirements. Many of the key procedures and functions of Windows 95 and Windows NT are encapsulated in DLLs.