A dynamic link library (DLL) is a special kind of executable file containing code that can be shared between several applications. Dynamic link libraries usually have a .DLL file name extension.

DLLs can either come with the operating system or with an application. The system code of &os2; itself is largely contained in DLL files, too, and can be found in the OS2\DLL directory on your boot drive.

"Dynamic linking" means that the code in the module is only loaded when some application demands it. If the code was already loaded by another application, it is reused. This has several advantages: