What is PIPE Interface in USB?

Does anyone here works with USB VIP? Can someone explain me what is PIPE interface?

I have a confusion whether PIPE mode is used to create interface between Data Link Layer and Physical Layer. (or) It is used to seperate the digital (encoding, scrambling) part with analog part in the Physical layer only.

Also, why most of the IP manufacturers purchase VIP with PIPE Interface instead of Serial Interface.

Thanks

In reply to mukul1996:

Search the internet or look here:
https://www.intel.in/content/dam/doc/white-paper/usb3-phy-interface-pci-express-paper.pdf