Carousel ads are an ad format by which several product images are displayed and rotate within the banner. The consumer can have interaction with each product.
The most often, carousel ads are used for site retarging. The products displayed on the banner are the products consulted on the merchant website and other product recommendations. In this case, each creative is dynamic and built on the fly for each individual (see programmatic site retargeting).
Carousel ads are also used for affiliate creatives. In this case, the affiliate chooses himself on the affiliate platform the products he want to promote.
An example of carousel widget for affiliates: