Straight Pipes Vs Stacks

I put a lot of miles on a K100 with 4 spring and air ride cab, yea, I don't want to have to do it again. lol

 

Wow, thatr looks identical to one of the ones I drove. lol

 

If there is a vertical stack behind the cab that has a muffler in it, which part exactly is considered „exhaust stack”? Just the pipe above the muffler or the whole vertical unit? Is there even a debate or is it a settled science?

Asking for a friend.

 

Anything vertical is "the stack". Think of other vertical stuff. A stack of boxes. A stack of books. A stack of unpaid toll invoices.