DLL Libraries

Dynamic Link Libraries (DLL) are an important structural component of Microsoft Windows. DLLs allow certain code fragments to be compiled into a single library, and to be linked to by multiple programs. This means that only one copy of the library needs to exist, and multiple programs can share the functions and the data between them. The difference between a DLL and a static library is that when you compile your programs, the DLL is not compiled into your executable, but instead remains a separate module. This feature helps to keep executable size low, and also allows for a DLL to be loaded into memory only when it is needed.

Source : Mera Windows