What is architecture photography?

what how do you define architecture photography, and what makes it so unique?
does it require a specialist?

First, it's "architectural photography," not "architecture photography."

Second, Google it! You'll get all the definitions and info you could possibly want.

One of the oldest and best photography firms
http://www.hedrichbles​sing.com/

Does it require a specialist?
Nope. It's like brain surgery. It only requires a specialist to do it well.

Often the purpose of hiring an architectural photographer is for marketing real estate. Within that subset, here's a nice site that may enlighten:
http://photographyforr​ealestate.net/

Architetural photograph is not simply pointing a camera at a building exterior or interior. Doing well means that the photographer often has to do things like these, in preparation for the shot...

• setting up camera to eliminate converging vertical lines
  
• choosing the best time of day/night to make shots
  
• light the building interior/exterior well...

  skillfully balance the many color temperature light sources that may be present (e.g. a shot could have daylight outdoor light visible, along with incandescent and fluorescent -- and combinations of severa; different temp fluorescents !)
  

  skillfully balance the relative intensity of different light sources...perhaps even masking windows the ND filters, so that interior and exterior details are more closely matched in intensity
  

  skillfully add supplemental light sources in the location, which compensate for inadequate illumination but which do not appear too obvious as added lights