An encyclopedia or encyclopaedia is a reference work or compendium providing summaries of information from either all branches of knowledge or from a particular field or discipline. Encyclopedias are divided into articles or entries that are often arranged alphabetically by article name and sometimes by thematic categories. Encyclopedia entries are longer and more detailed than those in most dictionaries. Generally speaking, unlike dictionary entries which focus on linguistic information about words, such as their meaning, pronunciation, use, and grammatical forms, encyclopedia articles focus on factual information concerning the subject named in the article’s title.
Encyclopedias have existed for around 2,000 years and have evolved considerably since that time as to 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 perceptions (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 production). As a valued source of reliable information compiled by experts, printed versions found a prominent place in libraries, schools and other educational institutions.
The appearance of digital and open-source versions in the 20th century has vastly expanded the accessibility, authorship, readership, and variety of encyclopedia entries and called into question the idea of what an encyclopedia is and the relevance of applying to such dynamic productions the traditional criteria for assembling and evaluating print encyclopedias.
Indeed, the purpose of an encyclopedia is to collect knowledge disseminated around the globe; to set forth its general system to the men with whom we live, and transmit it to those who will come after us, so that the work of preceding centuries will not become useless to the centuries to come; and so that our offspring, becoming better instructed, will at the same time become more virtuous and happy, and that we should not die without having rendered a service to the human race in the future years to come.