What is DLL file?

DLL stands for Dynamic Link Library and DLL files are modules that contain functions and data that can be used by other programs or DLLs.

DLL files allow programs to share common functionality and reduce memory usage. They also enable programs to interact with the Windows operating system and its components.

For Example: 
A DLL file can provide access to a printer, a graphics card, a network connection, or a database.

DLL files usually have the extension .dll, but they can also have other extensions, such as .ocx, .drv, or .cpl