I have a small question about third party. I am just trying to get clear understanding of it

If Mr.X is Working with Company A and Company A has direct Client XX. is Client B considered as Third party?

Or

Mr.X>Company A> Company B> Client XX. Now in this case Client XX is considered as third party?

How couldn't understand how USCIS defined the third party? I am just trying to know. Please help

So which one of above cases Client XX is considered as third party?