An encyclopedia is a collection of knowledge. Often, in an encyclopedia, there is an article related to events, things, social facts, social phenomenon, science topics, and so forth. Encyclopedias can cover a large array of knowledge.
Historically, most encyclopedias were printed on paper. Today, most are on the internet, though there are a few that still print physical copies or distribute digital media. The terms "internet encyclopedia" and "online encyclopedia" refer to any modern encyclopedia that can be found online.
encyclopedia (n.) 1530s, "course of instruction," from Modern Latin encyclopaedia (c.1500), thought to be a false reading by Latin authors of Greek enkyklios paideia taken as "general education," but literally "training in a circle," i.e. the "circle" of arts and sciences, the essentials of a liberal education; from enkyklios "circular," also "general" (from en "in" + kyklos "circle") + paideia "education, child-rearing," from pais (genitive paidos) "child" (see pedo-).
Modern sense of "reference work arranged alphabetically" is from 1640s, often applied specifically to the French "Encyclopédie ou Dictionnaire raisonné des Sciences, des Arts, et des Métiers" (1751-65).