For depth of field in photography, the smaller the number, the larger the opening. A picture is worth a thousand words. In this case, the background is less important and the subject is focused on. It usually has to do with pictures of people or pictures of nature.
A lot of movies and television shows use it to put emphasis on something intense or important.
In this case, it’s used for a commercial. The other Cokes are the exact same and just as tasty and important but the Diet is standing out in this picture to appeal to people that it’s “healthier”.
Picture taken from: flickr.com
