What is the difference between the concepts of "the territory of Tang Dynasty" and "the territory of China in Tang Dynasty"?

For ancient times, the correct statement should be the territory of the Tang Dynasty. This concept is relatively clear, that is, the area actually ruled by the Tang Dynasty. In the Tang Dynasty, the territory of China was vague. For example, Turkic, Uighur and Tubo don't belong to China, so it's hard to say. Of course, Tubo is better. After all, many of them are in Tibet, not to mention other ethnic minorities.

Besides, what is China? At that time, there was probably no such concept, only the concept of Middle-earth or Central Plains.