What/Where are "App Backup Files" System Junk?

Avast says there is ~12 GB of “App Backup Files” as System Junk. What are these files? Better yet, where are they located so that I can eyeball them?

Cheers.

… to clarify, I’m wondering if I should NOT delete these “Backup Files”. Are they Windows app backups that I create? Are they iOS device backups I store on the local drive?