What is a "PIT file"?

Both Heimdall and Odin have options for a PIT file. From Heimdall's option you can find, > Action: print-pit > Arguments: [--file ] [--verbose] [--no-reboot] [--stdout-errors] [--usb-log-level ] > > Description: Prints the contents of a PIT file in a human readable format. If a filename is not provided then Heimdall retrieves the PIT file from the connected device. And, from Odin there is a specific tab for it, when you click on the tab it says, > Do not use this tab. This tab is for engineers. You device will be changed with the pit in the CSC file. So what is a PIT file, and where is it documented anywhere? Can I generate one automatically?