No Idea because never used it.

SEO stand for Black Hat SEO and White Hat SEO
Black Hat SEO:not follow all the rules for Google provides. some black hat seo technique are below
(1)keyword stuffing
(2)cloaking
(3)doorway pages or gateway pages
(4)Hidden Text
which is some black hat seo technique

A. keyword stuffing
B. doorway pages
C. incorrect keyword
D. link farming

This is also one of the SEO techniques. such as keyword stuffing, duplicate articles, etc.

Black hat SEO refers to all the black techniques that gives short time results by doing too much over optimization of a website which in not good. Building bad backlinks, copy content, lack of on-page factors and more. All the activities which is banned by the Search Engines doing that is Black hat SEO.

Black Hat Seo=unethical techniques for seo and not follow all the guidelines for google.There are some Black Hat Seo Technique are below:
keywords stuffing, cloaking, doorway page or gateway page, hidden text etc

Black Hat SEO Techniques is not most essential for SEO. But IF you want get site rank increase so you can do it but site will not stable in search engines.

Black Hat SEO:-

Doorway pages
Cloaking
Keywords Stuffing
Hidden Text

Black hat SEO is the use of methods that are undesirable to search engines to increase a pages position in search results. These methods are intended to trick search engines into giving pages advanced positions in search results, and they have no benefit to site visitors

Black Hat
 

Black hat SEO is usually a practice that increases a page's rank browsing engines through ensures that violate the research engines' terms involving service. The term "black hat" came from Western movies to tell apart the "bad guys" from your "good guys, inch who wore white-colored hats (see white-colored hat SEO). Not too long ago, it's used more commonly to describe pc hackers, virus makers, and those which perform unethical activities with computers.

I believe that nowadays there is no white seo, all of seo turned black, if it goes for google at least

Black Hat SEO is designed for short term ranking but for lasting ranking.

It's the shortcut and wrong way of way . Nobody should do it . Otherwise there is a chance that google can banned your site .

Black hat SEO, one of the process to increase SERP very fast but it is not advisable to follow. Even search engines may penalize your website if it got stick with this method.

This really is a fast and easy way to get the best possible rates of traffic in the web. However, you have to take note that its ways are totally illegal.

black hat seo mean when you do some short cut work for backlinks or keywords ranking of you site. like hidden text, auto redirection, keywords stuffing, and many more