Webspam goes by many names (spamdexing, linkspam, black hat SEO, etc.) and refers to the practice of, or sites that engage in the practice of deliberately trying to manipulate search engine rankings through unethical techniques or those that go against search engines webmaster guidelines or terms of use.
This includes but is not limited to techniques such as:
Link networks
Article spinning
Using scraped or stolen content
Anchor text manipulation
Hacking / injecting links into sites
Comment spam
Hiding text on the page