Forro is a popular dance in Northeastern Brazil, as well as a type of music which accompanies the dance.
There are three explanations about the history of the word forro.
The first theory is that it is derived from the English expression "for all" in the early 1900s. While building the Great Western Railroad, the English engineers were throwing balls on weekends for railroad personnel or for everybody ("for all"). Most Brazilians will tell you this story.
The second theory states that the word is derived from forrobodo, which means "great party". The Brazilian folklorist Camara Cascudo, who studied the Brazilian Northeast came up with this theory. Forrobodo is believed to come from the word forbodo, which was used in the portuguese court to define a dull party.
The third theory tells us that the word is derived from the number of the engine that the English engineers used, "40" or " Four-oh" that was corrupted by the Brazilians into "Forro".