The term, commonly credited to Forrester, matters because it separates what a customer declared from what you merely observed (first-party) or bought from someone else (third-party). It is one of the highest-intent inputs for personalization, and permission is clearer in the act of giving it, though consent still needs to be captured and governed.

In practice

Zero-party data only works if the customer sees the loop close. If they tell you they shop for gifts under 100 euros and the next message ignores it, the question becomes a tax on their attention rather than a reason to share more.