Wiktionary
n. An entity that resembles a nation or a state, but which for the most part exists only on paper, on the Internet, or in the mind of its creator.
Wikipedia
A micronation, sometimes referred to as a model country or new country project, is an entity that claims to be an independent nation or state but is not recognized by world governments or major international organizations.
Micronations are distinguished from imaginary countries and from other kinds of social groups (such as eco-villages, campuses, tribes, clans, sects, and residential community associations) by expressing a formal and persistent, even if unrecognized, claim of sovereignty over some physical territory. Several micronations have issued coins, flags, postage stamps, passports, medals, and other items. These items are rarely accepted outside of their own community but may be sold as novelties to help raise money or collected by enthusiasts.
The earliest known micronations date from the beginning of the 19th century. The advent of the Internet provided the means for people to create many new micronations, whose members are scattered all over the world and interact mostly by electronic means, often calling their nations "nomadic countries". The differences between such Internet micronations, other kinds of social networking groups, and role playing games are often difficult to define.
The term "micronation" to describe those entities dates at least to the 1970s. The term micropatrology is sometimes used to describe the study of both micronations and microstates by micronationalists, some of whom refer to sovereign nation-states as "macronations".