What is the period of time that carrier_down_count represents?

Is the integer output the number of times the link has been down since 00:00 server time, in the last 24 hours or what exactly? The kernel.org site only provides this information: What: /sys/class/net//carrier_down_count Date: Jan 2018 KernelVersion: 4.16 Contact: [email protected] Description: 32-bit unsigned integer counting the number of times the link has been down

Details