What is the meaning of the saying of the Messenger of Allah, peace and blessings be upon him: "That which separates lawful from unlawful is the duff and the voice in marriage"? And what is the meaning of "duff" and "ghazal" mentioned in the context of permitting chanting and ghazal at weddings?

The Hadith was graded as Hasan (good) by Al-Albani and Al-Arna'oot. Its meaning is the announcement of the marriage and its mention among people with voice and the beating of the duff (tambourine). The purpose of this is to publicize the marriage by beating the duff and the voices of those present with congratulations or the recitation of permissible poetry. Some people take this to mean listening to music, which is a mistake.