Meta keywords are a comma separated list of keywords or key-phrases coded into web pages for the purpose of telling search engines what the content of each page on your website is about.
Over the years this has been abused by spammers and unscrupulous SEO companies by over-stuffing with repetitive keywords and even using popular keywords that were nothing to do with the actual page content. As a result meta keywords are now worthless so search engines use more sophisticated techniques to identify the subject matter of your web pages and what keywords they contain.
Search Engines work hard to try to be human when indexing web pages and rely more on on-screen factors such as the page content, titles and links. They invest heavily on identifying spam and finding your site blacklisted is no easy thing to recover from.
We have known for a while that Google do not use the meta keywords field at all, and where Google go - others usually follow.
There is some evidence that the search engine Bing is using the meta keyword field, but not for identifying keywords, instead it is used as an indicator that the page may be spam.
We will no longer include the meta keywords field in all new sites we build and recommend you don't use them at all.
So don't waste your time on meta keywords, use it to create fresh, unique and interesting content - that's what your visitors want to read - and what search engines want to index.