Keyboard Density is the percentage of times a keyboard or phrase appears on a webpage compared to the total no of word on the page in the context of search engine optimizations ,keyboard density  can be used to determine weather a web page to relevant to a specified keyword or keyword phrase.  

Once upon a time there when putting lots of keywords was the guarantee.But today this type of formula don't work. You have seen that there are lots of articles and blogs which even rank on keyword on which it is not optimized for. The number of times a keyword in a blog or article is called keyword density . The keyword density must be 0.5-1%.

Once upon a time people when putting lots and lots of keywords was the guaranty of ranking. But today this concept.was does not work you have seen that a blog and article on which it is not optimized. The number of times keywords spread on an article is called keyword density. The keyword density must be between 0.5 -1% according to yoast plugin .