A piece of content created with the primary purpose of attracting inbound links.
Linkbaiting comes in many forms, although determining if a particular piece of content qualifies as linkbait, and whether that is a good or bad thing, is subjective.
In the earlier days of the web, site owners noticed that certain types of content generated an inordinate amount of inbound links, especially from the blogsphere and influential sites like Digg. That gave rise to a flood of content that was increasingly formulaic, the most blatant of which spurred the name linkbait.
Although the term linkbait is often used derisively or accusingly, in reality, all content creators would like to find an audience for what they publish. Thus, learning the ins & outs of what makes content linkworthy has value.
see also: Digital Marketing Tools
Effective Link Bait Examples and Techniques
StayOnSearch (February 23, 2010)
An Introduction to Linkbaiting
ProBlogger (September 19, 2006)