From the dawn of the world wide web until the late 2000s, Meta Keywords used to be the goto way to get search results. The Meta Keyword Tag resides in the <HEAD> of an HTML document. The tag, only seen by search engines, looks like: <meta name="keywords" content="keyword, keyword phrase, keyword etc... and is not visible to the viewer. Therefore the Meta Keywords tag could be used to injected keywords into an HTML page without having any resemblance of the keyword in their content. Allowing you to lie to search engines!
Keywords were initially used for search engines to quickly look at HTML pages and store small amounts of data in their search index databases. At the time they were not crawling and storing cumulative information about HTML pages and websites simply because it was timely and expensive. It was only a matter of time before computers got faster and file storage got cheaper. Now Search Engines are using these keywords to sniff out spam.
Meta Keywords Denounced
In 2009, Matt Cuts posts on the Google Webmaster Blog
"Our web search (the well-known search at Google.com that hundreds of millions of people use each day) disregards keyword metatags completely. They simply don't have any effect in our search ranking at present."
In July 2011, Duane Forrester of Bing officially denounces the use of meta keywords on WebMasterWorld as a spammer technique
"I'll make this statement: meta keywords is a signal. One of roughly a thousand we analyze... Getting it right is a nice perk for us, but won't rock your world. Abusing meta keywords can hurt you."
In 2012, the question "Meta Keywords, should we use them or not?", was asked in the SEO MOZ (the leader in organic search) community. The question was responded to in unison.
"Actually Google does not mention anything about meta keywords only that they do not use this as a ranking factor. Bing however looks at this as an attempt to manipulate their SERPs. Also, using meta keywords will give your competitors a free link research goto for your site. I would not recommend using them."
What does this tell us about Meta Keywords?
Do not use Meta Keywords! Focus on great body content; let the search engines work for you. It's not a bad idea to consider removing meta keywords that were used in this fashion on older sites that you manage.
Write great content and engage in social media, and search engines will reward you.