What is black hat seo?

[anoopsh00]

Hidden Content
Meta Keyword Stuffing
Doorway or Gateway Pages
Link Farming
Cloaking(Hide flash animation from Google.)

[jordan25i]

Back Hat SEO techniques mainly include
keyword stuffing
cloaking
link baiting
link farm
hidden text link
door way page creation

Black hat SEO can give you quick improvement in ranking but it do not stand for long and if search engine catches it you website will be removed from index.

[iconwebservices]

Black hat SEO are prohibited by search engines or in violation of their Terms of Service.
Techniques are:

1.Cloaking.
2.Sneaky redirects.
3.Keyword stuffing.
4.copy content.
5.Copy links.
6.Pop ups and Pop under.
7.orphan page.