Hi, I think that In Search engine optimization, Black Hat SEO refers use to SEO strategy, Technics and tactics focus only on search engines like as spam comments, duplicate content, Article spinning, Keyword stuffing and invisible text etc.
Search engines have some guidelines to prove worthy for websites. If someone don't follow these guidelines and use of aggressive SEO strategies, techniques and tactics that focus only on search engines and not a human audience, and usually does not obey search engines guidelines.
Black hat SEO refers to a set of practices that are used to increases a site or page's rank in search engines through means that violate the search engines' terms of service. The term "black hat" originated in Western movies to distinguish the "bad guys" from the "good guys," who wore white hats (see white hat SEO). Recently, it's used more commonly to describe computer hackers, virus creators, and those who perform unethical actions with computers.
Spamdexing is the deliberate manipulation of search engine indexes. It involves a number of methods, such as link building and repeating unrelated phrases, to manipulate the relevance or prominence of resources indexed, in a manner inconsistent with the purpose of the indexing system.