What is the meaning of the padlock icon in Manage Backups?

Following the discussion in this AskDifferent post ("Is it safe to delete the contents of Library/Application Support/MobileSync/Backup if using iCloud?"), on my MacOS machine with Catalina, the finder switched to the device management mode when I just connected any iPhone to my machine and clicked on the name of the iPhone in Locations on the left of the finder window. Then I was pleased to see that clicking on "Manage Backups" under this phone's information display brought up a window listing backups from multiple devices, not just this iPhone.

However, I don't understand the meaning of the padlock icon next to one of the devices in the list. In fact, this was the one I wanted to delete, and I could proceed to delete the backup for this device, despite the padlock being shown. So then, what does the padlock icon signify, in this context? In the screenshot below, I circled the padlock icon in red.

The lock sign indicates that the backup is encrypted and protected by a password set previously against an unauthorized restoration of it to an iPhone. That is, you need to know the password for that backup to be restored to an iPhone if and when necessary. You don't need to know the password, however, to remove the backup as you also indicated.

See this Apple Support article titled "About encrypted backups on your iPhone, iPad, or iPod touch" for more details.