Following an internal report by the Bing team which has determined that providing annotations on ads can improve click through rates – Bing has introduced a feature called Dynamic Sitelinks. I would re-write to you what they do however the Bing blog post describes it best:
Dynamic Sitelinks is another way to help your potential customers evaluate what your web site has to offer prior to clicking through, which saves them time and provides you more relevant customer opportunities. However, dynamic sitelinks is an ‘annotation’, which means that Bing Ads dynamically creates the content for you from content already on your page.
Or in visual terms, this:
What’s great about this is that Dynamic Sitelinks does all the work for you. Content that’s highly relevant to a user’s search query is pulled from your ads’ landing pages through the Bing algorithm and is turned into annotations like the ones above. These aim to provide your potential customers with a sneak peek at some of the more specific information that they’ll find, should they click through to your site.