Keyword density refers to the amount of keywords within your website and pages in relation to the amount of content. Keywords are important for SEO purposes as they determine the topic and theme of a website and therefore what it appears in Google SERP (Search Engine Results Pages) for.
Getting the correct ratio between keywords and other content is crucial in conducting a successful SEO campaign. If your chosen keywords do not appear in the website or page often enough then the site will not be optimised to make an impact on Google search results. Conversely, repeating keywords too often is even more damaging for your SEO campaign as this is deemed as an unethical or ‘black hat’ form of SEO which brings with it harsh Google penalties.
It is good practice to use keywords approximately two or three times in each article or web page you create. There is lots of advice which says that between 1% and 3% of an article can be keywords; so this means that a 500 word article can have between 5 and 15 repetitions of your chosen keywords. Repeating them that many times within such a short piece of writing will not make the article flow correctly for readers and can come across as ‘spammy’ so it is best to stick to just a few repetitions and focus on quality, not quantity.