This counter displays the total number of threads that have been recognized by the CLR since the start of this application; ...

This counter displays the total number of threads that have been recognized by the CLR since the start of this application; these threads have a corresponding .NET thread object associated with them. These threads are not created by the CLR; they are created outside the CLR but have since run inside the CLR at least once. Only unique threads are tracked; threads with same thread ID re-entering the CLR or recreated after thread exit are not counted twice.