What is meant…scrape music source before import library?

Hello,
My Kodi on older Raspberry Pi is slowed, lagging, and skin failing to load properly so yet again I am going to reimage the program on the memory card.
But my library is so very large that I don’t want to spend another whole day recreating it.
I want to export the library (in multiple files I understand) and then import it into the refreshed program. I see the instruction, “scrape music source”. What does that mean? I think I have everything else clear. The music source will not change at all….2 hard drives in a dock.
Thanks for any tips.