This counter displays the number of threads that are currently recognized by the CLR; they have a corresponding .NET thread ...

This counter displays the number of threads that are currently recognized by the CLR; they 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.