What it is
A practical definition
A prompt sets the model's role, the rules and the answer format; prompt engineering is the work of making that answer controllable and useful in a given scenario.
Example in ecommerce
On a product page the prompt can require answers grounded only in store data, comparisons across key specs, and a closing line that points to the next step toward purchase.
Business impact
Cuts the share of vague answers, keeps recommendations consistent and raises dialogue quality at the commercial points of the journey.