PIFs, or Program Information Files, define how a given MS-DOS program should be run in a multi-tasking environment, notably to avoid giving it unnecessary resources which could remain available to other programs. TopView was the originator of PIFs which were inherited and extended by DESQview and Microsoft Windows, where they are most often seen. PIF's are seldomly used today in software due to the absence of MS-DOS applications.
Within Windows, a PIF holds information about how Windows should run the application the PIF corresponds to. The instructions can include the amount of memory to use, the path to the executable file, and what type of window to use (Full screen, window, size in pixels).