Restored from previous forum. Originally posted by FonkFonk.
AFAIK, a DLL is a file that contains resources that are used by an executable only when needed (to avoid loads of data being loaded in memory during execution of a program), for instance icons (see your Windows "moricons.dll" file you use to associate an icon to a shortcut), or mathematical functions you wouldn't find in the commands "library" of a compiler( e.g, specific Windows functions you would find in Windows DLLs, not to forget third parties DLLs).
Hope this can help !
Pierre