A reference work is a compendium of information, usually of a specific type, compiled for ease of reference. That is, the information is intended to be quickly found when needed.
The writing style used in these works is informative; the authors avoid use of the first person, and emphasize facts. Indexes are commonly provided in many types of reference work. Most are updated as needed, typically with a new edition each year.
In libraries, these works are typically not allowed to be checked out.