Dynamic-link library (also written as Dynamic Link Library or DLL), is Microsoft's implementation of shared libraries used by the Microsoft Windows operating systems. These libraries usually have the file extension DLL, OCX (for libraries containing ActiveX controls), or DRV (for Windows legacy system drivers).

Any of the Microsoft Windows data files having the same file format as that of the Dynamic-link library can be called a resource DLL. Examples of such DLLs include icon libraries, sometimes having the extension ICL, and the font files, having the extensions FON and FOT.

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