Utopia is the name of a book. Thomas More wrote it in 1516. He wrote it in Latin. Its original title is De Optimo Republicae Statu deque Nova Insula Utopia. This is usually translated to On the Best State of a Republic and on the New Island of Utopia.
The book is about an island with an imagined society. In the book, a visitor to this island tells about his trip there. According to him, Utopia has a system of laws that is perfect. Society there is also perfect. The political system is so good that nothing better can be thought out. Today, the word utopia is used to refer to a society that is unrealistic, and impossible to make.
There were several attempts to create such perfect societies (They did not work). The word utopia can also refer to a society of such an attempt.