Keyword density is the percentage of times a keyword appears on a web page compared to the total number of words on the page. While keyword stuffing is the practice of inserting a large number of keywords into Web page content and meta tags.Keyword stuffing is considered an unethical SEO technique.
A canonical tag is HTML element that helps webmasters prevent duplicate content issues occur when the same content is accessible from multiple URLs. Canonical tag can also be useful to solve www and non www canonical issue.