A reference designator indicates where a particular printed circuit board assembly (PCBA) fits on the board within the BOM.
A PCB has two unique part numbers. The first part number Is stamped on the board and is used to identify the blank board without any components. The second part number is typically printed on a label and identifies the finished board with all the different components.
*Source: https://www.youtube.com
Read our best practices articles for tips on effective and efficient bill of materials (BOM) management.