Black Hat Seo is the process to obtain high rankings for a website by exploits weaknesses in the search engine algorithms. This type of a method of SEO does not follow the SEO guidelines of search engines. The wholesomeness level of Black Hat Seo is very low. Blackhat SEO has a high amount of risk and delivers the short lasting growth.
Black Hat SEO is most commonly defined as a disapproved practice that nevertheless could increase a page's ranking in a search engine result page (SERP). These practices are against the search engine's terms of service and can result in the site being banned from the search engine and affiliate sites.
Link velocity is the rate at which others are linking to your site. Building quality backlinks should be the main priority, not achieving a high link velocity. However, link velocity is one of the SEO metrics that you should track.