Where does “чалга” come from?

чалга (Bulgarian) comes from Turkish çalgı, from Turkish çalmak, from Proto-Turkic čal- — to mow.

чалга (Bulgarian): chalga music genre, based on a peculiar Oriental-styled playful rhythm and motifs drawn from Bulgarian folk and partly from Greek, Serbian, Turkish, Romani and Arabic music, usually accompanied by a kind of dance related to belly dancing, known for its provocative lyrics