Ederlezi is the Tzigane (Gypsy) name of the Serbian Saint George, whose feast day is the 6th of May.
As a name, Ederlezi comes from the Turkish word Hidirellez. It is the name given to the early spring holidays. It is made from the names of two prophets, Hizir and Ilyas. Hizir is the protector of plants and poor people, while Ilyas is the protector of animals and waters. The legend says that they were friends and they drank the Water of Immortality. Then they swore to see each other on the night of every 5th May in order to give life back to nature. Hidirellez is a very important day in Asia Minor. The Slavs from the Balkans added the Christian aspect which came from St George's Day.
As a song, the origin of Ederlezi is a little more controversial. It is sometimes introduced as a traditional Tzigane song. However, its huge popularity dates from an arrangement by Goran Bregovic for the 1988 film Dom za vesanje (Time of the Gypsies), directed by Emir Kusturica - see this clip from the film. The lead vocal on this version was by the Macedonian singer Vaska Jankovska.
There is also a Serbo-Croat version of Ederlezi recorded around the same time by the Yugoslav folk-rock band Bijelo Dugme (White Button), for whom Goran Bregovic played guitar. In this version (as in almost all "pop" covers) the lyrics are not the same as those we know from Bregovic's more famous arrangement.
There are thousands of covers of Ederlezi, in all sorts of musical styles, some fairly tasteless! The Boban Markovic Orkestar's version is an interesting one, in a Balkan brass band arrangement. Here is an acoustic version for two female voices and guitar, by Roxane, Thilou & Feile, and at the other end of the scale a huge Bulgarian TV production with traditional costume and an orchestra.
And this is the Gurt Lush version.