Identify all <iframe> content on the page. There is a policy set up in Siteimprove to help with this called "Find iframes."
If the <iframe> contains readable or viewable content (i.e., is not a container for analytics scripts that the user won't interact with), he <iframe> must have a title attribute with a short description of the contents.
If the content is video or audio content, the title should represent the title of the media.
Otherwise, the title should represent the embedded content. (The page title of whatever is embedded for example)