When a product is defective or doesn't work as promised, it's called a lemon. The term comes from the fact that lemons are sour and not really enjoyable to eat. Just like a defective product, they're not something you want.
There are a few different things that can make a product a lemon. First, it might not work at all. This could be because of a manufacturing error or because the design is flawed. Second, it might not work properly. This could be because it breaks down often, doesn't do what it's supposed to do, or just doesn't meet your expectations. Third, it might have serious defects that make it unsafe to use. These defects could be discovered after you've already owned the product for a while.