Do you know what a region is? It's like a specific area or place that has its own rules and people in charge of making those rules happen. Now, a special administrative region is when a country (like China) decides to give a specific region within their country a little bit more freedom than other regions.
So, let's say China decides to make Hong Kong a special administrative region. This means that Hong Kong can have its own government and political system (like an election) that is different from the rest of China. It also means that people in Hong Kong may have different rights and freedoms than people who live in other parts of China. For example, in Hong Kong, people have more freedom of speech and freedom of the press than people in other parts of China.
Basically, a special administrative region is like a special club within a bigger club, where the members have some unique rules and privileges that other members don't have.