Depending on what you want to do, many kinds of bikes can be used for touring, not just "touring bikes". Touring bikes typically feature:

* long wheelbase (favoring stability over responsiveness)
* long chainstays
* large number of braze-on mounts (often three water bottle mounts and mounts for front and rear racks)
* relaxed geometry (favoring comfort over efficiency)
* upright position for the rider (favoring comfort over efficiency)
* heavy-duty construction
* lower gearing (typically comparable to the gearing on a mountain bike)

These features are nice to have, particularly if you are carrying all your stuff (tent, sleeping bag, camp kitchen, food, water, clothes). If you already have a bike (for example, a mountain bike), you can generally repurpose that bike for touring with only a few adjustments at most. If you decide that you like touring, you can then get a touring bike that fits your needs.