What is a signed system volume?

macOS includes enhanced protection for your Mac with cryptographic technology (macOS 11 or later) that prevents access to or execution of files that don’t have a valid cryptographic signature from Apple. All system files are protected on the signed system volume (SSV). This advanced system volume technology provides a high level of security against malicious software and tampering with the operating system.

It also allows software updates to complete in the background while you work, which reduces the time it takes for your Mac to restart and complete updates.