Final answer:
The term for when a celebrity or authority figure promotes a product is the testimonial advertisement.
Step-by-step explanation:
When a celebrity or authority figure promotes a product, it is called the testimonial advertisement. This type of advertisement relies on the credibility and trustworthiness of the celebrity or authority figure to persuade consumers to buy the product. It is a common marketing strategy used to leverage the fame and influence of well-known individuals to endorse and promote products.