An encyclopedia is a work of reference, containing a number of articles that deal with a specific topic or else a range of subjects. An encyclopedia is typically found in printed form or as an online database. Encyclopedias are distinguished from other books and websites by a number of defining characteristics, which have drawn people to consult them in their various forms for reference.
Readers depend on an encyclopedia to enable them to find information quickly and easily. Since the encyclopedia is likely to contain many entries, especially if it is written on a range of subjects, the encyclopedia will be well-organized. Typically, it will make use of an index, often at the back of the volume or on the website's homepage, for readers to look up entries of interest. The encyclopedia might also be organized thematically, with each category containing a separate index.
Encyclopedias represent an array of knowledge contained in one place; even encyclopedias composed to address one theme or topic will typically have many entries that go into great detail. Since assembling this knowledge requires a large vessel, printed encyclopedias tend to be in huge volumes, or even multiple separate volumes that form a whole. Online encyclopedias typically contain an extensive network of pages.
People turn to encyclopedias to answer questions, and so encyclopedias need to be a source of facts and clearly articulated explanations that can settle disputes and help readers. Encyclopedias are thus written in as clear and direct a way as possible to avoid confusing the reader. Some encyclopedias also become known for providing answers to certain kinds of questions. For example, the Guinness Book of World Records provides facts about extremities of human life, and so a reader would know to look to this encyclopedia to discover the height of the world's tallest man, for instance.
Encyclopedias are temporal in nature, and need to be constantly updated to avoid the information contained within becoming obsolete. This is especially the case with scientific and medical encyclopedias, which cover fields where theory and practice is continually being improved and rethought. Online encyclopedias are thus updated regularly, while printed encyclopedias have traditionally been released once each year or every other year to address changes since their last volume.
In many cases, encyclopedias are compiled by experts in a particular field, who write each entry and ensure that the facts contained within are correct. For example, "Hardy Trees and Shrubs: An Illustrated Encyclopedia" is a text with contributions by the respected horticulturist Michael A. Dirr, as noted by the Flower Expert website. This lends authority to the encyclopedia and strengthens its worth as a reference tool for individuals with an interest in gardening.