Meta keywords are one of three tags related to search engine optimization located in the source code section of the page of a website.
Over the years, the meta keyword tag has become fairly worthless, particularly with Google, Yahoo and Bing. Other smaller search engines may still be using the meta keyword tag as an indicator of what the page is about.
When search engines first came on the scene, they would use the meta keyword tag to determine, in part, what the content on the page was about. Website owners (and SEO’s) began “stuffing” the page with lots of keywords, most of which were not even relevant to the content on the page, but as a way to attract search engines to list their page.
We still see websites today that have 20 or more keywords in the meta keyword tag, which indicates the site was probably part of this trend 10 years ago. If your website does not have a meta keyword tag, that is OK too. We use it to see how relevant the words you put there are to the content on the page. If you do have the tag and plan on keeping it, limit it to 5-10 words max.
If you have a blog, you can repeat the words you have as tags in the post to the meta keyword tag. Blog tags are essentially a modern version of meta keyword tags, except they force you to list words that are relevant to the post.