A snippet is simply a listing in a search engine results page. An average results page is made up of 10 snippets, each usually displaying the title, link and a description of the page being listed.
So what’s a rich snippet? Simple – a it’s an ordinary results listing that has been enhanced with additional information. However, thinking just about Google, there are a lot of variations, and they often change the formats and types of rich snippets they display.
However, common examples include a simple star listing and review information inserted under the site’s link to much more detailed information about the content you’ll find on the page, including images and videos.
It’s also important to note that although Google frequently uses specific mark-up on the page to generate the listing, they can put together rich snippets from general information that they find. Also, having the correct mark-up to generate a rich snippet does not guarantee that Google will grace your site with one. As with everything Google, it’s really down to their discretion.
One final note – don’t confuse rich snippets (or even simple) snippets with other types of content that can appear on a results page, such as adverts, product, image and video listings, maps and local results, answer boxes, etc. As you can see, SERPs are a complicated place these days!