Micronations, microstates, imaginary countries, countercountries, unrecognized nations, or ephemeral states, are all terms for countries which have been declared independent by (usually eccentric) individuals or small groups, but unlike other such attempts, fail to achieve widespread diplomatic recognition. Many have only one inhabitant; others are larger. Most seem to consist of a single Grand Poobah, with or without a coterie of petits Poobahs. Talossa, however, counts over 50 citizens who have been part of its wild multiparty political structure. And there are reportedly 20,000 people with Hutt River citizenship or honours--more than several members of the UN!
In most cases, Micronation founders have declared dominion over land that actually exists; often tiny, isolated islands, sometimes under several feet of water. Like other countries, some of these nations have proclaimed declarations of independence, adopted constitutions, sought diplomatic recognition, sent out envoys extraordinary and ministers plenipotentiary, displayed coats-of-arms, and issued stamps, passports, and currency.
You can even become a citizen of an existing micronation!