The meta description tag exists as a short description of a page’s content.
Search engines do not use the keywords or phrases in this tag for rankings, but meta descriptions are the primary source for the snippet of text displayed beneath a listing in the results.
The meta description tag serves the function of advertising copy, drawing readers to your site from the results. It is an extremely important part of search marketing. Crafting a readable, compelling description using important keywords (notice how Google bolds the searched keywords in the description) can draw a much higher click-through rate of searchers to your page.
Meta descriptions can be any length, but search engines generally will cut snippets longer than 160 characters, so it’s generally wise to stay within in these limits.
In the absence of meta descriptions, search engines will create the search snippet from other elements of the page. For pages that target multiple keywords and topics, this is a perfectly valid tactic.
Not as important meta tags
Meta Keywords: The meta keywords tag had value at one time, but is no longer valuable or important to search engine optimization. For more on the history and a full account of why meta keywords has fallen into disuse, read Meta Keywords Tag 101 from SearchEngineLand.
Meta Refresh, Meta Revisit-after, Meta Content-type, and others: Although these tags can have uses for search engine optimization, they are less critical to the process, and so we’ll leave it to Google’s Search Console Help to discuss in greater detail.