This is chocolate that comes in a bar. It's solid and is usually melted and then incorporated with other ingredients. It comes in different varieties of sweetness, or as I usually use it: unsweetened. There's a huge range of quality for this ingredient. A good guide is to use the best quality that you feel is affordable. The difference in quality has to do with the type of cocoa beans used, the choice of additives which make it possible for the beans to turn into a solid bar, and of no little importance: the process by which the beans are turned into a solid bar of chocolate. I've found Ghiradelli to be a good all around choice, though some of the more expensive brands I've used have produced more spectacular results. For some of my more mundane baking, I've used Baker's with very tasy results as well. You can have a little fun shopping for this ingredient!