Dynamic Link Libraries, or DLLs, are modules that can be dynamically loaded and linked to an application at runtime. DLLs contain executable code, data, and resources that can be shared across multiple programs. These are essential for the efficient operation of modern Windows operating systems. However, there are other synonyms for dynamic link libraries. Some of these include shared libraries, loadable libraries, and runtime libraries. Shared libraries are similar to DLLs but are found in UNIX-based systems. Loadable libraries, on the other hand, are used for Mac OS X. Finally, there are runtime libraries that are an essential part of any programming environment, whether Windows, Unix, or Mac.