Learn Dutch: Dat is niet jouw zaak. - That is not your business.

We normally use geen to negate a noun that has no article or uses een (a or an). However, because the noun zaak has the possessive pronoun jouw (your) in front of it, it becomes a specific, definite noun. To negate a specific noun, we must use niet.

Why does this sentence start with dat instead of die?

When pointing out a general situation, concept, or unnamed thing as that, Dutch always uses dat, even if the noun that follows later in the sentence is a de-word (like de zaak).

Could I use je instead of jouw in this sentence?

Yes, you can say Dat is niet je zaak, which is completely correct. However, using jouw puts extra emphasis on the word your, implying that it might be someone else's business, but it is definitely not yours.

Does zaak always mean a commercial business or shop?

While zaak often means a shop or a company, in this expression it translates to business in the sense of a personal matter, affair, or concern. You will also see it used in legal or police contexts to mean a case.