Encyclopedia

An encyclopedia is a reference work or compendium providing summaries of knowledge, either general or special, in a particular field or discipline. Encyclopedias are divided into articles or entries that are arranged alphabetically by article name or by thematic categories, or else are hyperlinked and searchable. Encyclopedia entries are longer and more detailed than those in most dictionaries. Generally speaking, encyclopedia articles focus on factual information concerning the subject named in the article's title; this is unlike dictionary entries, which focus on linguistic information about words, such as their etymology, meaning, pronunciation, use, and grammatical forms.

Encyclopedias have existed for around 2,000 years and have evolved considerably during that time as regards language (written in a major international or a vernacular language), size (few or many volumes), intent (presentation of a global or a limited range of knowledge), cultural perspective (authoritative, ideological, didactic, utilitarian), authorship (qualifications, style), readership (education level, background, interests, capabilities), and the technologies available for their production and distribution (hand-written manuscripts, small or large print runs, Internet). As a valued source of reliable information compiled by experts, printed versions found a prominent place in libraries, schools and other educational institutions.

In the 21st century, the appearance of digital and open-source versions such as Wikipedia (together with the wiki website format) has vastly expanded the accessibility, authorship, readership, and variety of encyclopedia entries.

The word encyclopedia comes from the Koine Greek ἐγκύκλιος παιδεία, transliterated enkúklios paideía 'general education', from enkúklios (ἐγκύκλιος) 'circular, recurrent, required regularly, general' and paideía (παιδεία) 'education, rearing of a child'; together, the phrase literally translates as 'complete instruction, complete knowledge'. However, the two separate words were reduced to a single word due to a scribal error by copyists of a Latin manuscript edition of Quintillian in 1470. The copyists took this phrase to be a single Greek word, enkuklopaideía, with the same meaning, and this spurious Greek word became the Neo-Latin word encyclopaedia, which was in turn borrowed into English. Because of this compounded word, readers since the fifteenth century have often, and incorrectly, thought that the Roman authors Quintillian and Pliny described an ancient genre. Following Noah Webster's spelling reform, the spelling of the word varies between encyclopedia in American English, encyclopaedia in British English (although the spelling encyclopedia is increasingly gaining acceptance), and encyclopædia in certain specialized cases.

The modern encyclopedia evolved from the dictionary in the 18th century; this lineage can be seen in the alphabetical order of print encyclopedias. Historically, both encyclopedias and dictionaries have been compiled by well-educated authors, but they are significantly different in structure. A dictionary is a linguistic work that primarily focuses on an alphabetical listing of words and their definitions. Synonymous words and those related by the subject matter are to be found scattered around the dictionary, giving no obvious place for in-depth treatment. Thus, a dictionary typically provides limited information, analysis or background for the word defined. While it may offer a definition, it may leave the reader lacking in understanding the meaning, significance or limitations of a term, and how the term relates to a broader field of knowledge.

To address those needs, an encyclopedia article is typically not limited to simple definitions, and is not limited to defining an individual word, but provides a more extensive meaning for a subject or discipline. The Merriam-Webster definition of encyclopedia states that it is "a work that contains information on all branches of knowledge or treats comprehensively a particular branch of knowledge usually in articles arranged alphabetically often by subject". In addition to defining and listing synonymous terms for the topic, the article can treat the topic's more extensive meaning in more depth and convey the most relevant accumulated knowledge on that subject. An encyclopedia article also often includes many maps and illustrations, as well as bibliography and statistics.

In addition, sometimes books or reading lists are compiled from a compendium of articles (either wholly or partially taken) from a specific encyclopedia.

Four major elements define an encyclopedia: its subject matter, its scope, its method of organization, and its method of production: