What is std::thread::hardware_concurrency returns?

I was experimenting with my mach laptop while reading C++ Concurrency in Action, one of the ver first examples is to identify the number of the actual hw threads with std::thread::hardware_concurrency(), which returns 8 on my machine.
But before printing std::thread::hardware_concurrency()I have made a type and printedstd::thread::hardware_concurrency which was 00B61410.

So what is the difference between std::thread::hardware_concurrency() and std::thread::hardware_concurrency? What does the later identify?