"5 over 1" Is it stories or fire code?

[Arlington]

This is probably a @datadyne question: what is the proper understanding of "5 over 1" ?
Or maybe the answer is "it has morphed" or "its understanding changed as it came to be widely used"

Is it:

• Architecture: N stories over a podium of P Stories (where N = 5 and P = 1)
• Fire code Type 5 (wood frame) over Type 1 (fireproof concrete)
  

 

[737900er]

I think it started with the Fire Code definition. Many early examples only had three wood-framed stories over the podium and today four wood-framed stories remains extremely common.