Link baiting is when you come up with a unique way to get links through developing cool content, tools, videos and so on. Link baiting gets its name from fishing. You bait your hook, you draw it into a pool of water where you know it is concentrated with fish, and you expect lots of bites. But you better (1) bait it with enticing food and (2) make sure your food is of the tastes of the fish. Same with link baiting. If I create a cool tool about how to cook pork, but I market it to Jews or Muslims, it won't get much attention.
Now, is this frowned upon by search engines? Is it a form of link manipulative link building? I don't think so? If your audience doesn't bite your bait then that is the determining factor. But if you create useful, and tasty bait, and your audience bites, then you deserve the reap the ranking rewards.
Forum discussion at Search Engine Watch Forums.