Backlinks — Links to your page from other sites on the Internet are called backlinks. Search engines use links to indicate general popularity. Search engines take into account where the link is coming from, which page it’s pointing to, and what the actual text of the link says.
Link Bait — Content that is posted to a web site with a controversial or inflammatory title or content, that is intended only to draw links and traffic. Most of the time this is used as a derogatory term for content that has no value except to get people angry or excited enough to link to or visit the content.
Link Farm — This is another black hat SEO technique. It involves setting up multiple sites whose main purpose is to contain links to other sites. This technique tries to take advantage of the relative importance search engines place on links. Changes to search engine algorithms have been made to detect and devalue these sort of links, rendering them useless from a ranking perspective.
The best way to get other sites to create high-quality, relevant links to yours is to create unique, relevant content that can naturally gain popularity in the Internet community. Creating good content pays off: Links are usually editorial votes given by choice, and the more useful content you have, the greater the chances someone else will find that content valuable to their readers and link to it.
(Google Quality guidelines)