Is this a broadax or a side ax ? How broad does a broadax have to be to be a broadax ?

I have been lead to believe that a broad axe has a bevel on both sides of the blade.   A side axe or shaping axe has only one side beveled, plus one entire side is flat and will lay flat on a table.   Especially for shaping logs into beams. 

Per Sellens the term broad axe and side axe can be interchanged but a side axe is usually a single handed axe and a broad axe is used with 2 hands. Many different blade/head patterns and different axes are shown in his book "Dictionary Of American Hand Tools"  under Axe pages 23 - 39.

It is indeed a broad axe. They are fitted with a curved handle  (to protect your hands ) and that handle can be fitted from either end of the unusual poll.

Yes, side ax and broad ax are two names for the same thing -- an ax or hatchet ground on one side, like a chisel.  I believe that side ax is a more British term while broad ax is preferred in American English.  Salaman also illustrates a "wheelwright's ax which is sharpened in this manner.  For some reason, American English uses side ax for the cooper's tool, but broad ax for the larger tool used for hewing beams.