DLL: Dynamically Linked Library. Pieces of software that are used by more than one application are referred to as "libraries". The process of combining a library with an application so they work together is called "linking". If a library is linked when the programmer is designing it, the library will be included in the application program file. When a library is stored in a separate file from the application, and is linked when the application is run, it is said to be "dynamically linked". Thus, a library which is linked when the program runs is called a dynamically linked library, or DLL.