SEO(serach engine marketing) is one of best internet marketing under the head of SEM(serach engine marketing). There are two techniaues of SEO. One is white hat seo and othere is called black hat seo. It is also called ethical and unethical seo. Which seo follow the policies and rules and regulaions of seo is called white hat seo. black hat seo is that which is not folllow the polices and rules and regulations of SE Keywords stuffing, invisable text and doorway pages are some tools of Black hat seo.