A classic “touring bike” is generally a road bike (i.e. drop handlebars) with relaxed frame geometry and a long wheelbase. Relaxed frame geometry means that the average rider -not necessarily a youthful athlete- is in a comfortable position that allows her/him to ride all day without having parts of their anatomy give out. The rider’s position and the bike fit are key to long distance survival.
A broader interpretation of a touring bike is really any bike you tour on. Many long-distance travellers use hybrids (700c wheels, flat bars with bar ends) or cross cross-country mountain bikes (26” wheels, flat bars with bar ends), and lots of Europeans use butterfly (many possible hand positions) handlebars. What’s important is that your set-up allows you to change hand positions and postures as you ride. This eases strain on various parts of your body and allows you to pedal more effectively into a headwind or uphill. You can go further.