IO to E193FPP 19" Flat Panel

Spec sheet does not describe the various connectors for which I would like to understand the purpose.  Following are what I see:

a 15 pin Analogo input (I understand use)

a DVI 24 pin with flat blade  (I understand use) 

two USB ( what use)

one 1/4 inch square with two diagonal corners much like USB to printer connector  (what use)

Appreciate ,

 Ed