An AI Overview is a summary Google may show in Search, with links to supporting websites. Google shows it when its systems judge that a summary adds value to the usual results.
For a business, an Overview creates another place where a source link may appear. Being cited does not guarantee a click, and an Overview may not appear for the same search every time.
Google says a page must be indexed and eligible to appear in Search with a snippet before it can be a supporting link. Ordinary search practices, such as making pages crawlable and helpful to readers, remain relevant. There is no special markup or AI file required for inclusion.
A featured snippet is a highlighted excerpt from one page in search results. AI Mode is Google's conversational search experience, where people can ask follow-up questions. Google says AI Mode and AI Overviews may use different methods and show different supporting links.