If it doesn't have a Brooks saddle, a
Yehuda-moon-worthy handlebar bag, and stuff bungeed to the racks, it's not a touring bike.
Seriously: You can, of course, tour on anything, including trikes, unicycles, etc. That said, ruggedness, comfort, the ability to mount racks, and gears low enough for climbing under load are the features that make touring more enjoyable.