How can the Silk Road be described as a social system rather than just a trade route?

If this is a question your teacher has asked you, or that is asked in your book, there are probably specific facts that you will be expected to know.  I would suggest you look for them in case the ones we provide aren't the ones in your book.

The general idea here is that the peoples along the Silk Road interacted with one another in ways that gave them something thin common.  So a person in what is now Uzbekistan would have the culture of the Silk Road in common with a person in China (assuming both were in cities on the Silk Road.)

The most obvious example of this can be seen in the Buddhist religion.  The religion was founded in India but spread along the road from there to China.

So the idea is that there are cultural ideas that would have spread along the road and that all the peoples along the road would have come to have in common.  Look for ideas like that in your book or notes.