SEO Glossary Definitions: Black Hat
Black hat is a term that is used in SEO usually to mean unethical. Black hat SEO techniques are those practices that are deemed unethical especially by the search engines, who take a dim view of such practices, while a black hat SEO is an SEO professional or SEO service that uses those techniques in order to try and gain an advantage over a website's main competitors.
When we refer to ethical SEO we talk about white hat SEO, and more recently the term grey hat has been coined to refer to those practices and services that fall somewhere between the lines of ethical and unethical. The fact is that it seems unethical or if it feels like you're attempting to manipulate the search engines into ranking your site highly without providing useful and informative content for your customers then it is likely that you are partaking in black hat SEO techniques.
Search engines, like good website owners, attempt to provide value to all of their visitors and users. They aim to do this by offering high quality content in their listings. A lot of effort is put in by certain search engines to help ensure that their index is clean and does not include spammers or sites that have evidently used black hat SEO techniques in a bid to outperform other, more beneficial websites. Ignorance is not deemed a valid excuse by the search engines meaning that you need to take care in all your actions and ensure that an SEO service uses only ethical practices when working on your behalf.