the difference between

Here is more than you ever thought you could know about barley: http://www.barleyfoods.org/consumer.html/.

I recommend soaking hulled barley overnight to reduce the cooking time, and I'm not sure if I'm imagining it or not, but I also think it improves the flavor and texture.

Hulled is more nutritious, has the hull removed but retains the bran. Pearled has hull and bran removed, is still fairly nutritious, though. Here is a good page on that, Cook's Thesauraus:
http://www.foodsubs.com/GrainBarley.html