A featured snippet is a Google result that puts the answer first and the source second. In a regular result, the title comes first and the snippet below it. According to Google’s explanation of featured snippets, Google’s systems decide per search whether a page is suitable.
You do not need markup for it, and you cannot nominate a page as a featured snippet yourself. Featured snippets can also appear within the People also ask block.
Example
A page that answers a question directly below the heading provides usable material:
## What is the difference between a quote and an invoice?
A quote is an offer you send before the job: what you will
deliver, at what price and on what terms. You send an invoice
after delivery, as a request for payment.How do you opt out?
With the nosnippet rule, both featured snippets and regular text snippets disappear for that page. Text with the data-nosnippet attribute is not used in snippets. A low value for max-snippet makes a featured snippet less likely, but Google writes that this is not guaranteed to work.
Common mistake
Adding structured data in the hope of getting a featured snippet. Featured snippets come from the text on your page, not from markup.
More in Writing content that AI assistants can cite and under SERP.