DLL stands for Dynamic Link Libraries.

They are like EXEs but cannot be run directly.

It is based on the Portable Executable file format. DLLs can also contain COM components and .NET libraries.

A DLL contains functions, classes, variables, user interfaces, and resources (like icons, images, files, ...).

A program loads a DLL on startup via the Win32 API LoadLibrary or when it depends on another DLL. A program uses GetProcAddress to load a function or LoadResource to load a resource.