Black Hat SEO is by my definition, using unfair techniques to drive results in search engine listings.  In most cases, however, using Black Hat SEO Techniques, the result is temporary leading to only short term gains.  There are risks involved in Black Hat SEO which may even involve getting banned.  Of course many of us have used Black Hat SEO at one time or another.

Some different Black Hat SEO Techniques

Stuffing Keywords: This would be taking a keyword such as “free stuff online” and repeating it over and over in your page in order to gain a better search engine position.

Stuffing Cookies: A method that causes affiliate merchants’ tracking systems to conclude that a user has clicked through a tracking link (and to pay commissions accordingly) even if the user has not actually clicked through any such link. If the user subsequently makes a purchase from that merchant — immediately, or within the “return days” period specified by the merchant’s affiliate program — the affiliate then receives a commission on the user’s purchase.

Invisible Text: Hiding text in the same color as the background.  This might work temporarily, but is definately not a good long term solution and will cause you to lose your pagerank.

Comic via ByronShell