Rich snippets
Rich snippets are search results that show more than a title and two lines of text — stars, prices, opening hours, expandable questions. They appear when a search engine finds structured data on the page and trusts it.
The basis is structured data: machine-readable statements in the source that tell a search engine what a piece of content means — that "6 pm" is an opening time and not a house number. Without that markup, a result stays a page with text on it.
One principle decides it, and most people trip over it: you may only mark up what a visitor actually sees on the page. Mark up reviews that appear nowhere and you lose the display — and, if you persist, the search engine's trust.
Even with clean markup it remains a possibility, not a promise: whether the data turns into an enhanced result is the search engine's decision, and it changes those rules regularly.