What is the difference between the various cisco numbers?

in CCNA & CCENT
PID VID - Part ID, Vendor ID
SN: Serial Number
PN: Part number
Serial numbers are used for logging tac cases. When is the part number, and PID VID used?
I really have no absolute clue.
SN: Serial Number
PN: Part number
Serial numbers are used for logging tac cases. When is the part number, and PID VID used?
I really have no absolute clue.