roasting vs baking
Why do you bake a ham, but roast pork? Turkeys are roasted, casseroles are baked. Apparently onions can be baked or roasted. They all go in the oven with the door closed and at the same general temperatures. Is there really a difference between baking and roasting, or is it more a common usage thing?
In current American English usage, the distinction between the terms is an inheritance from the ages before the modern home oven/stovetop. Roasting, strictly speaking, was done in front of a fire (often on a spit, either vertical or horizontal or angled), in a hearth, where the roasted item had free air circulation. Baking was done in enclosed spaces (not just ovens, but also covered pots).
Today, roasting generally refers to baking (1) at higher temperatures, and (2) where the item is raised on a rack so that there is complete air circulation around it. It's an approximation of genuine roasting but it's really a form of baking.
So, we tend to use the term roasting for things that once were subjected to genuine roasting.
Barbara Kafka wrote an entire book on roasting and she said one of the hardest parts of writing the book was trying to come up with a definition of roasting and how it differs from either baking or pot roasting. After discussing the subject with a number of chefs and other cookbook authors, she concluded that temperature and fat were the differentials. Roasting is usually at a higher temperature (although I'm sure she'd get an argument on that from Paula Wolfert author of "The Slow Mediterannean Kitchen") and includes fat--even if it's just natural fat rather than added fat.
I'd say baking was a more general term, referring to all kinds of oven cooking, including cakes and things cooking in a sauce.
If you tell me you'e roasting something, I assume you're using a hot oven, with no liquid and probably a coating of fat on whatever you're cooking, and I assume you want it to emerge browned and carmelized outside.