Normal and inferior goods are classification given by economists to to goods judging on their behavior.
Normal good is the most common type. It is said a good is normal when it's
consumption increases when the income increases. Like clothes, when your income
increases you buy more clothes.
The opposite happens with inferior goods, of which consumption decreases when
the available income increases. For example, used books and instant noodles:
the more income you have the less used books and noodles you buy.
A normal good is a good that a person will be more likely to buy the higher
their income becomes. An inferior good is a good a person will be less likely
to buy the higher their income becomes.