Greater China refers to a geographical region that includes China, Taiwan, Hong Kong, and Macau. It is also referred to as the Chinese-speaking world because Mandarin Chinese is spoken in most parts of this area.
Imagine that you and your friends from different neighborhoods decide to come together and form a big group. That's sort of like what happened with Greater China - a bunch of areas with some similarities came together to form a bigger, more powerful region.
China is the biggest and most populous country in Greater China. Taiwan is a smaller island nation located off the coast of China, and Hong Kong and Macau are both special administrative regions that have been allowed more freedom than other areas of China.
Even though these areas are all located close to each other and share some similar cultural features, they are also different in some important ways. For example, people in Taiwan speak a different dialect of Mandarin Chinese than people in mainland China. And Hong Kong and Macau were both colonies of European countries (Britain and Portugal, respectively) for many years, so they have some unique cultural practices and systems.
Today, Greater China is a very important economic and political region, with a lot of trade and exchange happening between the different areas.