[AZLiberty]

For me:

A Dreadnought or Jumbo is a "large guitar"
000 or OM is a "medium size guitar"
00, GA, 0, Parlor, or smaller is a "small guitar"

To be a "Travel Guitar" it would have to be smaller than an 0/Parlor, something like the Little Martin or Baby Taylor would count, neither of which can hold a candle to a Parlor sized instrument sound wise.

(IMHO of course)

A bigger guitar like the Voyage-Air is obviously a "travel guitar" by function.