Headway is the distance and time between two buses or trains that are going in the same direction. Think about it like a game of follow the leader with cars. When the first car moves, you have to wait a certain amount of time before you can move your car so that you don't crash into the first car. That amount of time is called headway.
In the same way, trains and buses need to have headway so that they don't bump into each other. When a bus or train leaves the station, it needs to travel a certain distance before the next one can leave. This is because if the first bus is too close to the second one, there could be a crash and that would be bad for everyone.
So, headway is important because it helps keep us safe when we are traveling on buses or trains. It also helps us get to where we need to go more efficiently because buses and trains with longer headway times can move faster and finish their routes quicker.