Search snippets are highlighted parts of documents returned by search engine
In search engines it's something like a teaser of a document you are searching for. It contains part of a document text with highlighted parts you're searching on.
For e.g.
when searching for dog you will get documents with highlighs
Dog was eating and sleeping at the same time
I was walking my dog out.
Snippets can contain also thumbnails of documents and other metadata.
