AKA DLL on MicrosoftWindows platforms. Unix platforms use a ".so" filename extension, for Shared Object.
A library of functions linked dynamically to an executable at RunTime. This makes the executable smaller since it doesn't have to include all that code, and also means less memory use, since all programs that use the same library can share the read-only code.
See the SharedLibraries? page for more.
One page links to DynamicLinkLibrary: