Keyword Density is the percentage of times a keyword or a word or a phase appear in a webpage to thew total number of words in that webpage. it should be 2-3% in an content. More than that consider spam by the search engine.
Keyword density is the percentage of times a keyword or phrase appears on a web page compared to the total number of words on the page. In the context of search engine optimization, keyword density can be used to determine whether a web page is relevant to a specified keyword or keyword phrase.