Reference books are encyclopedias, directories, and other similar books designed for east access to information. They are handy and informative, so use them as a starting point for your research. It's a quick way to find out important names and events, get ideas for keywords to use in online searching, and get an overview of your subject.
Most of the print reference books listed below are located on the first floor just above the Pit. Dance books generally are under the numbers REF GV1580-1799.4. Some are in the Ref Stacks on the third floor, however; just look at the call number if you aren't sure. Be sure to ask the person at the desk if you have any difficulty finding these books!
These two reference databases below are used primarily for research in music. However, since music and dance are closely related, these sources have a lot of material about dance as well. Give them a try with your topic!