I looked it up recently and found that it is actually a legitimate SEO technique. In short, any content that encourages other webmasters to link to you can be considered link bait - hence the term. :)
The following are the more common link baits:
- Great Content. Write great content, or be an authority on a subject, and webmasters will link to you.
- Humorous, Cute Or Weird Content. If your content is real good, you can get a lot of people linking to you from the social bookmarking sites.
- Controversial Content. Never fails to attract a lot of debate, traffic and hopefully, backlinks.
- Tool. An online tool is a good way to get a lot of backlinks. Examples would include html checker, calculators to convert from one unit to another, some kind of graphics generator, etc.