Utopia is the title of a book by Thomas More, the name is derived from the Greek, meaning "Nowhere". A fictional depiction of a rationally organised society, the title has since been used as a generic word to describe both works of fiction in which the author's theories of a better way to organise society are dramatised, and actual communities founded in attempts to put such theories into practice. The theories generally revolve around a more equitable distribution of goods, frequently with the total abolition of money, and citizens only doing work which they enjoy, leaving them with ample time for the cultivation of the arts and sciences. The sewers in a utopia never need unblocking.
The utopia may be usefully contrasted with the dystopia.
Examples of utopias:
The section in Gulliver's Travels by Jonathan Swift depicting the calm, rational society of the Houyhnhms, is certainly utopian, but it is meant to contrast with that of the yahoos, who represent the worst that the human race can do.
A large number of books by H.G. Wells
Aldous Huxleys book Island. (His most famous work, Brave New World could perhaps be considered a utopia, as the people in that society are certainly happy, but it is more generally regarded by critics as a dystopian satire, as they actually have no choice in whether they are happy or not.)
The Dispossessed, a science fiction novel by Ursual K. le Guin. sometimes said to represent one of the few modern revivals of the utopian genre, though it is notable that one of the major themes of the work is the ambiguity of different notions of utopia.