Black Hat SEO can be defined as the the practice of using unethical techniques to improve our search engine rankings.These activities are considered to be spammy activities and the people who do this activity are called the spammers. Google Search Engine is very alert about it and time to time releases updates like penguin, panda etc. to punish those sites by dropping their ranking in the SERPs. Some of the black hat techniques are cloaking, door way pages, keyword stuffing, content hiding or making it invisible etc. Every SEO must chose the white hat techniques for achieving long and sustainable ranking of their site.