What is the meaning of the phrase "what it is they do"?

My name is Tam - from Vietnam. Call me Tim if you like. I just saw this phrase in my English course book and not sure what it means. The phase is "what it is they do". Could somebody please give me a clue? Thanks so much!


Solution 1:

as an Italian I feel the sentence “what it is (that) they do”? as a calque of the Italian "cosa è che fanno".. probably introduced in the English language in the USA by Italian immigrants.. In Italian it sounds fine and understandable.. in English it sounds horrible, and probably "what they do" is sufficient...