A dynamic-link library (DLL) is a library of functions, data, and resources whose references are resolved at run time rather than at compile time.

Applications that use code from static-linked libraries attach copies of that code at link time. Applications that use code from DLLs share that code with all other applications using the DLL, therefore reducing application size. For example, you might want to define in an ObjectWindows DLL complex windowing behavior shared by a group of your applications.