File extension for a Dynamic Link Library file. These files are used by the operating system as and when it needs them thereby saving RAM, e.g. a printer has driver .dll`s which do not need to be in the RAM during editing. Windows calls on the driver at the time of printing. (Note: dll files can have other extensions such as cpl, exe or ocx).
Dynamic Link Library. Files which are sub-programs to larger programs and are tied together. DLLs are accessed by programs only when needed. This helps reduce the size of an executable program.