What are tributary states?

A state that is subordinate to a more powerful neighbor. It was a form of subordination in pre-modern times.

A tributary state is a state which is subordinated to a more powerful neighbor state. It was a form of subordination in pre modern times.

Explanation:

The tributary state sent a regular token of submission to the superior power state. This was a tribute, a substantial gift of wealth, such as the gold produced, or slaves. The tribute may be seen as the payment of protection money. But there were other ways to show submission as well.