Bohemians are inhabitants of Bohemia, now part of the Czech Republic.
Inhabitants come from both Czech and German stock, due to Bohemia's position on the borderlands between Germany, Austria, and the Czech Republic and its history, which includes rule by earlier incarnations of each of these countries. Because of the many changes in government and the resulting population migrations, one cannot say with complete confidence that a Bohemian is a German or a Czech. In fact, the Boii, for whom the land was named (by the Roman Empire), were a Celtic people, who moved westward. Since then, the inhabitants of the area have been predominantly Slavic.
A secondary meaning for the term Bohemian emerged in early 19th century France. The term was used to describe a group of artists, writers, and disenchanted people of all sorts who wished to live a non-traditional lifestyle. See the article Bohemianism for more on this.