Link bait is any content or feature, within a website, designed specifically to gain attention or encourage others to link to the website. Search on google. I have been reading wiki for details. That's very helpful.
Matt Cutts defines link bait as anything "interesting enough to catch people's attention." Link bait can be an extremely powerful form of marketing as it is viral in nature. The content for link baiting would be a text, image, audio or video clip and it interesting enough to catch the people’s attention.