Which NTP concept indicates the distance from a device to its authoritative time source?

Stratum indicates the distance, or "hops," from a device to a primary, authoritative time source. A stratum 0 device is a highly accurate reference clock (like a GPS receiver or atomic clock). A stratum 1 server is directly synchronized to a stratum 0 device. A stratum 2 server synchronizes with a stratum 1 server, and so on. Lower stratum numbers indicate more accurate and reliable time. NTP peer refers to another NTP-enabled device with which a device exchanges time information. GPS and atomic clock are examples of highly accurate time sources, often serving as stratum 0 devices, but they are not the concept that describes the distance.