The snippet is the text under the title link. Google may use your meta description, or extract text from the page, whichever better matches the query. Query-specific extraction is common and usually helpful.
Controls
nosnippet, show no snippet at all.max-snippet:[number], cap the character count.data-nosnippet, exclude a specific HTML element from snippets.max-image-preview,max-video-preview, control media previews.
Featured snippets
A featured snippet is an answer pulled to the top of results. You cannot mark up for one; Google selects them algorithmically. Pages that earn them tend to answer a specific question directly, near the top, in a paragraph, list or table.
Alien Road recommends: answer the question in the first two sentences under the relevant heading, then elaborate. This is good writing regardless of snippets, the reader gets the answer immediately, and it happens to be the structure Google can lift cleanly.