A normal good is one which is governed by the amount of money a consumer has in a straightforward way. With normal goods, more money means more demand. Restaurant meals and DVDs are examples of normal goods. As consumers acquire more money, they will spend more money eating out or buying movies on DVD.
An inferior good is a good judged as having low quality. The chief attraction of an inferior good is the price. As consumers gain more money, they will actually tend to spend less money on inferior goods. Some examples of inferior goods are generic clothes and fast food. A poor consumer will buy generic clothing to save money and seek out fast food because it is a cheap way to dine out. If that consumer unionizes and gets a better salary, he will not spend more money on fast food or generic clothing. Instead, he will tend to shift to name-brand attire and sit-down restaurants, spending less money on inferior goods.
A luxury good is one on which a consumer will spend not only more money, but a greater percentage of his income as his income increases. High-end jewelry, expensive collectors' items and plasma televisions are all luxury goods. Luxury goods are also normal goods, but many normal goods are not luxury goods. For example, a consumer may spend more money on DVDs as he makes more money, but may not spend a greater percentage of his income on them, which makes DVDs a normal good but not a luxury good.