The number of times a keyword is used in some blog post or webpage is called keyword density. All search engines have their own rules/guidelines in this regard. For example, Google, the largest search engine in the world, allows 1% to 3% in content. So i advise you to check your target search engine's latest guidelines in this regard thoroughly.
In case you don't abide by the guidelines related to keyword density, the search engines will treat it as keyword stuffing. In this case, your website can get penalized.