A keyword is a word that is going to be placed in your article several times, not just once as that would make every word a keyword. Keyword density is a crucial part of optimizing your articles for search engines. But it is important to note that there is also such a thing as over-optimizing your articles for particular words, this is known as keyword stuffing.
When you over-optimizing your article with stuff keywords in an article a search engine spider will detect that you are trying to trick it into placing your article high in the search engine results for that word, and will instead punish your site and your page for doing such. This may even affect the rankings of your other pages or get your site blacklisted from a major search engine if you are found keyword stuffing too many times.
Keyword density is how many times your keyword is placed in your article. Most use a percentage to determine how many times they will put a keyword in an article. For instance, if you have a 400-word article and want to achieve a keyword density of 6%, then you will need to have the keyword in your article exactly 24 times. An effective article must have a keyword density between three until eight percent of the overall article. If you use very high density and over optimize your article search engine will mark your article as spam.
Having the right keyword density in your article makes it more likely that you will make money off of that article because it will go up in the search engine results and be seen by more people. But you must remember please be careful when you optimize your article don’t over optimize your articles with very high keyword density, you will get your site blacklisted from a major search engine.