Inferior goods are things that people buy less of when they have more money. This is opposite to normal goods, which people buy more of when they have more money.
For example, imagine you really like hot dogs. But if you suddenly got a big raise at work and had more money, you might start buying fancier foods like steak instead of hot dogs. So, hot dogs are an inferior good because you buy less of them when you have more money.
In general, inferior goods are usually things that people buy because they are cheap and affordable. When people have more money, they can afford better quality or more expensive things, so they stop buying the inferior goods as much.