"If someone asked you to build a coffee table and they specified the legs as a height of 50, what do you think that would mean? 50 kilometres? 50 feet? 50 inches? 50 millimetres? Probably 50 centimetres. You can’t know for sure, but you can guess, based on the table’s intended use — 50 kilometres, 50 feet, and 50 inches are way too big for a coffee table, and 50 millimetres is way too small."
Marc does a great job at explaining color spaces for developers, and non-devs as well. If you're a developer who deals with color at all, I highly recommend you read these posts.