What are the “things” that ebb and flow

Ebb and flow (also called ebb and flood and flood drain) are two phases of the tide or any similar movement of water. The ebb is the outgoing phase, when the tide drains away from the shore; and the flow is the incoming phase when water rises again. The terms are also common in figurative use. Hope this helped! :)

The ocean is one, I'm pretty sure a car tire is another