Rich snippets are search results that contain more information than just a meta title and a meta description. With the help of a rich markup, a search engine can display this extra information in the search results.
The information displayed in a rich snippet makes the link stand out from all other search results. This is how you distinguish yourself from competitors, because your information immediately attracts the attention of visitors. You can think of reviews, images, contact details, products from a webshop (for example, the product feed from Google Shopping), the number of stars or extra information about an event.
Be careful with the use of rich snippets. Search engines regularly check the information in rich snippets to prevent abuse. Bots check if the content of the page matches the information in the rich snippet. Invisible or misleading information is penalised by Google, which does not help search engine optimisation.
Besides rich snippets, there are also turbo snippets and featured snippets.