A Responsive Display Ad is an ad that automatically adjusts its size, appearance, and format to fit available ad spaces on the Google Display Network, where it can be seen on millions of sites on the internet. It leverages the text and image assets you provide it and uses machine learning to show users the best asset combinations. In other words, Responsive Display Ads are highly flexible and do the heavy lifting in terms of optimizing your ads. Because these ads reconfigure themselves using the assets you provide, they can fit into more available ad inventory on Google’s Display Network, maximizing your reach.
The text assets are headlines (max. 30 characters) and descriptions (max. 90 characters), while the image assets are ad images and logos. Other optional assets you can provide are videos. It is recommended to provide as many assets as you can, so that Google has more to work with to optimize your ad’s performance. The maximum number of headlines and descriptions are 5 each. You can also upload up to 15 ad images and 5 logo assets.
There are requirements for the text and image assets you can use, which you can find out more about here.
To give you a better idea of what different responsive display ads look like, here are some examples of multiple formats: