Dynamic Search ads are those ads which target searched based on the content of given Landing page. We generally write the ad text for these ads and headlines are dynamically created.
Also, these ads are a great help when advertising for multiple products since for each new product added you need not work on the keyword set.
Dynamic Search Ads are ads based on the content of the website and don’t have keywords or landing pages. It involves creating ad groups and ads. Matching to user’s query will happen taking into consideration the content of the website.
The headline in an ad will be dynamically populated that means no control over it however the description lines can be defined. The landing page the user will land on is again decided by google based on the web domain specified in the campaign settings. Such campaigns greatly help in an industry or the domain where pages added dynamically as per the user growth.
Hope this helps.