What can you say about the custome used in ethnic dance?

You keep asking about ethnic dancing. The way your questions are phrased make it clear that you are supposed to have studied all this already, and that the answers are in your text book or in the notes that you took during class.

And do you mean "customs" or "costumes"?

Very varied across the world. 

Note spelling: costume.

Note that some 'ethnic' costume is authentic, but some is purely for the tourists.

They have a good beat and you can dance to them. Ethnically.