Keyword density and placement are important parts of optimizing your articles for search engines. Search engine spiders scan a page in a way that makes it important to place your keywords where they will be detected and recognized as a keyword, so that your article will come up when someone searches for that keyword.
What is a Keyword?
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. When a spider sees that you have a word placed several times in an article, it will determine that your page may be useful to users that search for such a keyword.
Over Optimizing Your Articles
It is important to note that there is also such a thing as over optimizing your articles for particular words, this is known as