What are HTML Keywords
Keywords in HTML are words that you are targeting on a web page. They are typically short phrases that represent what the page is about. They are also, hopefully, the words that someone might type into a search engine and find your page.
In general, HTML keywords are found whether you intend them to be there or not. Keywords are just text like any other text, and when a search engine views your page, they look at the text and attempt to make a decision regarding what the page is about based on the text it sees.
Meta Data in HTML
<meta name="keywords" content="keywords,html keywords,meta keywords,keyword data" />
This meta tag is not very important. Most search engines don't use the keywords meta tag because it can be manipulated so easily by the web page writer. In other words, many page writers used to put random keywords into the keywords tag, in the hopes that the page would be optimized for those (probably more popular) phrases.
A More Important HTML Meta Tag Than Keywords: Description
If you are going to include meta data on your web pages, you should ignore the keywords tag, and instead use the meta description tag. This is meta data that nearly every search engine uses to describe your web page in their index. And that extra information could mean the difference from a customer clicking on your site for information or someone else's.
HTML Keywords and Search Engines
Instead of using the keywords meta tag, you should think about keywords in the actual content of your web page. These are the terms that the search engines will use to evaluate what the page is about, and thus where it should appear in their search results. This allows you to first write content that is useful, and then focus on search engine optimization to optimize that content for the keywords you are focusing on for that page.
How to Choose HTML Keywords
When you are choosing the keyword phrase for a web page, you should first focus on just one phrase per web page. It is not a good idea to try to optimize one web page for many different things, as this will confuse not only the search engines, but more importantly your readers.
One strategy that may seem counter-intuitive, but works well for many sites is to choose “long-tail” keywords. These are the keywords that don't get huge amounts of search traffic. Because they aren't as popular with searchers, they aren't as competitive and it's possible to rank higher in search for them. This gets your site noticed and gets you more credibility. And as your site gains credibility it will start ranking higher for more popular terms.
HTML Keywords Generators and Other Keywords Tools
Another way to determine the keywords in your HTML is to use a keyword generator. There are many online tools that will analyze your web page content and tell you how many times various phrases are used on your page. These are typically called keyword density analyzers. That previous link shows you some free ones that I have found, or you can check out keyword density tools recommended by other About.com readers.