Business hotels are much cheaper than regular hotels. They tend to be located near stations, convention centers, and facilties where meetings and events are held. The rooms tend to be much smaller and less "plush" than regular hotels. For example, there may be a refrigerator in the room for your use, but it may not be stocked; the room may be carpeted, but not with plush shag; the bathroom will probably be a small unit-type shower / sink / toilet. The rooms are generally designed for 1-3 persons.
If you are travelling on a budget and are alone or with just a small group, business hotels are a good option. You can sometimes get discounts for reserving rooms in combination with train or plane tickets (ask a local travel agent), and / or for online reservations.