What is robot. txt. and keyword density?

Web site owners use the /robots.txt file to give instructions about their site to web robots; this is called The Robots Exclusion Protocol.

Keyword density is a jargon term in SEO that refers to the number of times your keyword phrase appears on the page. At one point, this did have an effect on search engine rankings, but updates by search engines over the years and changes in how people use the web have dramatically changed SEO best practices, including how keyword density should be used (if at all).

Robots.txt is a text file that lists webpages which contain instructions for search engines robots. The file lists webpages that are allowed and disallowed from search engine crawling.

Keyword density is the ratio (or percentage) of the number of times your keyword appears on the page of your article, versus the number of words on the page.

Robot.txt is the text file it tells the search engine which pages of the website allow for crawl or not crawl, and you can also can give the code which search engine want to crawl your website, the all control you can give in robot.txt

keyword density is one of the seo on-page factor, the keyword density should be 3-4% only more then this percentage you optimize the keywords in the webpage is penalized, so keep 3-4%  of  keyword density in all webpages in your website.

Keyword density is the percentage of times a keyword or keyword phrase is found in your page content amidst all the other content. For example, if you have a Web page with exactly 100 words on it, including all headlines, captions, alt text, and advertising, and you have a keyword phrase that is on the page 3 times, your keyword density is 3%:
Robots.txt is a text file that lists webpages which contain instructions for search engines robots. The file lists webpages that are allowed and disallowed from search engine crawling.