WMF
In Windows, a metafile is a file that contains information regarding one or more other files. Called a Windows Metafile Format (WMF), it is commonly a graphics file format, containing information for vector graphics or bitmap files. The WMF contains a list of function calls that Windows uses in its Graphics Device Interface (GDI) layer to display images on a computer monitor.
The WMF was originally released around 1992 as a 16-bit format file for Windows 3.0. A 32-bit version was released in 1993 and called an Enhanced Metafile (EMF). For Windows XP, the Enhanced Metafile Format Plus Extensions (EMF+) format was released. There are also compressed WMFs, called Compressed Windows Metafile (WMZ) and Compressed Windows Enhanced Metafile (EMZ).