Ask HN: How to explain what adaptive websites are to your clients?

We make websites for clubs, mostly sportclubs. We have been creating a master adaptive template for this clubs. However, our customers are not always up to date on the latest technologies. Still, we need to convince our customers why they should choose an adaptive website. Simultaneously, we need to explain what an adaptive website is in simple language.

How would you explain to someone unfamiliar with the matter what adaptive websites are. And how would you convince them it is the way to go?