This is a list of Core IDs denoting the so called relative "quality" of cores from best to worst one. During manufacturing process some cores might be of slightly better quality and reach the targeted operating points (frequency) at a slightly lower voltage. Note that the difference is quite small and even the "worst" core is still of high quality and reliability. The ranking is relative and can be different for each CPU.
This information is available on later Intel and AMD CPUs and is displayed either in the main window under the CPU node, or in sensors as (perf #) for each core.