From Webopedia : In search engine optimization (SEO) terminology, black hat SEO refers to the 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.
Blackhat is the technique which do not follow rules and regulations.
There are two reason why you may report black hat SEO. Either your
website has been attacked through a malicious hack, virus or negative
SEO campaign of spammy links, or you see spammy web results on a
competitive keyword your website is ranking on. For the latter, you may file a webspam report
through Google Webmaster Tools. Please use this tool with discretion.
SPAM does not stand for search positions above mine! Falsely reporting
web spam could be considered black hat SEO.