Gray hat SEO is the combination of White hat and Black hat SEO, this is maximumly done by newly learned SEO persons, because they are unaware of what ais black hat and white hat. But practicing this grey hat is risky.
Gray hat SEO is SEO techniques that take more risks than white hat SEO techniques but aren't likely to get your site banned from search engines (although a search engine penality could result). They're questionable SEO techniques but not in the same category as black hat SEO techniques. However, what's considered gray hat SEO today might be black hat SEO next year.
Gray hat seo is called mixture of black and white, and it is panalysed by search engine so i will sugget we should not use gray hat seo should technique, and one thing more later it could be turn in to black hat seo and be a reason to be banned your website.