There are several hidden tags that can be included in websites which search engines can use in various ways.
A page’s title tag is what shows up in your browser’s tab and as the heading in search results. Most search engines will use this on all your search results and it is a slight ranking factor.
This is typically the name of the page followed by the name of the website, such as “Properties to Buy – John Doe Real Estate”
This is a tag that visitors cannot see by actually going to your website, instead it is only seen by search engines who can choose to use it in some situations. It generally isn’t visible in search results as the search result description is automatically generated by the search engine based on what content on the page reflects the user’s search query most accurately. The Meta Description is only used when the search engine cannot generate a more relevant description for some reason.
Adding a Meta Description is especially useful for pages without a significant amount of text content on the page, such as some homepages with lots of images and not much text.
The description is not used for any ranking by any major search engine and cannot affect how high a page shows up in search results. If used, it will only be displayed in the search results.
Meta keywords was a tag designed to assist the early search engines in the 90’s by listing keywords that were relevant for the page. This was needed because back then search engines didn’t have a lot of processing power to do any sophisticated analysis on the page like they do today.
No search engine today even bothers to read this tag and it has zero ranking influence. Search engines analyse the page its self for keywords rather than relying on (easily abused) keyword lists provided by the website owner. Search engines have not used this tag in any way since approximately the year 2000. Google has never used the tag and other search engines quickly adapted when Google came on the scene.