Rich results snippets are a type of search result that provides more information than a traditional text-based snippet. They are designed to give users a preview of the content of a page and help them to understand whether a page is relevant to their query. Rich results snippets can include a variety of different types of information, such as images, reviews, ratings, and more. Some examples of rich results are reviews, recipes, articles, events, and many other types.

    To be eligible for rich snippets, a webpage should follow the guidelines and technical requirements provided by the search engine. Those guidelines usually include proper structured data markup on the page, which is a set of tags added to the HTML of a web page to provide information about the page to search engines, in a format that they can understand and process. Structured data also needs to be valid and formatted according to the specifications provided by the search engines.

    Google, for example, supports structured data in JSON-LD, Microdata and RDFa formats and has a structured data testing tool to help the website owners to check their markup.

    It's worth noting that not all webpages will be eligible for rich snippets, and even if they are, it doesn't guarantee they will be shown in the rich snippets format. The search engine algorithm also uses many other factors to determine the relevance and quality of the webpage to the user's query.

    Using rich snippets can greatly improve the visibility and click-through rate of a website, since they make the result stand out among the regular snippets and make it more likely to be clicked.