How do you define "traffic" in block traffic from/to in Rules?

I have set up my vlans. Now it is time to define the flow of traffic. I see that in Rules, I can define "block traffic from" or "block traffic to." I wonder what is the definition of "traffic" here. For example, if I block traffic from network A to network B, does that mean no IP packets can flow from network A to network B? Or maybe no TCP connection can be from A to B (which means there are still IP packets from A to be)? Does it also mean no UDP packets can go from A to B? I appreciate your response.