What does Keyword Density mean?
This is a hotly debeated concept in the world of SEO. The general idea is that a page on the internet about "cars" should contain the word "cars" fairly often if search engines are to believe it is about "cars".
The keyword density calculation is a percentage of how many times that word appears on the page. So for example if a page contains 100 words and the word "cars" is mentioned 6 times then the keyword density for "cars" on that page is 6%.
However if it contains the word "cars" at a rate of more than 4-6% of the time in the text search engines may conclude the page is trying to scam it's way to the top and should be penalised with lower rankings or removed from the search engine index completely.
Different words, same meaning
First of all it is important to know that search engines understand words with the same meaning. So they understand SEO and Search Engine Optimization are one and the same. Use both 4% of the time on a page and you are actually saying the same thing 8% and heading for hot water!
Does keyword density matter
Always consider it a part of SEO. There are many top ranking websites that do not have any particular keyword density for the words and phrases that they rank for. This is simply because there are other ways to get to the top than using Keyword Density.
You should also not that how the keyword is presented on the page has a strong affect. So if it is in a heading tag
or in any anchor text
it will be given more weight and importance than if it is just in the text.
As such, and as best practice, any keyword should be in the heading tags and in the main body of the text but the density should be no more than between 4-6% of the overall text.