How much is a cup of vegetables?

Often, we read that you need to have a cup of veggies form the vegetable group and so on. But what exactly is meant by a cup of vegetables? Well, if you are using raw or cooked vegetables, then a cup means exactly that much - that means one cup of raw or cooked vegetables equals a cup of veggies. This hold true for vegetable juice as well. But if you are using raw, green, leafy vegetables then 2 cups of these would equal one cup of vegetables. This is what I have been able to find. I would appreciate if you could share anything you know about this.