Hostellers, referred to also as backpackers (especially in Australia and New Zealand), are people who travel on a budget, often changing city every few days. They tend to travel for long periods, with the minimum equipment they require, since after all they have to carry it on their shoulder. They usually travel by train, bus or even hitch-hike, and are looking for a difference experience of the places they visit from the average tourist.
They usually are more keen on learning about the actual lifestyle of the people of the country they're travelling in, rather than just sightseeing. Monopolizing on this experience of lifestyles, many of these backpackers have taken a year or more off just to travel the world and experience what it has to offer.