Hulu is an online television site. You can watch old shows like Lost in Space, The Big Valley and Barney Miller.
Or you can catch up on shows you missed, like Bones. Fox had allowed a few of their shows to stream on Hulu, but the other networks were lagging behind.
Now ABC is streaming some of their shows (on a day-by-day rollout) on Hulu! This is so great! I would watch ABC shows on their own site, but I prefer Hulu's interface. For one thing, ABC's video stops at the end of a commercial and you have to manually start it again.
Now I'll be able to watch Lost straight through! Woot!