It refers to a brief list of the most important keywords and phrases of your webpage. They are a specific type of meta tag that appears in the HTML code of a Web page. These tags are different from regular keywords as they appear "behind the scenes" in the source code of your page instead of the live, visible web page. They are not visible to the users like your meta titles and meta descriptions.
However, at present, Google does not consider meta keywords in its ranking algorithm as they are too easy to abuse. They are devalued by Google as they were misused by site owners and marketers. For example, stuffing the code with high-volume keywords and phrases to rank low-quality pages, which dilutes the accuracy and quality of search results.
Meta keywords are placed in the HTML code of the webpage. They tell search engines which keywords your page is optimized for. To write meta keywords, scan the copy on your page and make a list of important words or phrases then shortlist ten to fifteen keywords which you think accurately describe the content of your page.
Some instructions to write optimized meta keywords are listed below:
Meta Keywords : Syntax