Google supports a small number of meta tags. Most of what is discussed as “meta tag optimisation” has no effect.
Used
<title>, not strictly a meta tag, but the most important element on the page.meta description, often used for the snippet; not a ranking factor.meta robots, indexing and serving directives.meta charset,meta viewport, encoding and mobile rendering.meta refresh, supported but discouraged; use a server redirect.google-site-verification,google: nositelinkssearchbox,google: notranslate.
Ignored
meta keywords has been ignored for many years. Author, revisit-after, distribution, rating and similar tags do nothing for Google.
Alien Road recommends: write descriptions for the click, not for the crawler. Google rewrites descriptions when it finds a better match for the query, so a keyword-stuffed description gains nothing and loses persuasion. We write them as ad copy: what the page gives, and why it is worth the click.