A model is anyone who is hired to help sell or drive up consumer demand for a particular product, service, concept, or brand. Everything from laxatives to cigarettes to clothing for special occasions; all use models to try and entice the consumer to purchase this or that product. That’s just business.
Models are generally very good looking people. For example, if you are selling Speedos, the last thing in the world you want to do is put a 400 pound man in your product. You want to put a svelte, ripped body builder in your product instead.
Celebrities can also serve as powerful models for a product, service, concept, or brand. If you have Miley Cyrus or Michael Jordan wearing your brand of jeans, you can rest assured sales for your brand of jeans will go through the roof. Or, if you have Bill Gates talking about your particular charity, you can rest assured the awareness of that charity will increase exponentially.