The second derivative is the rate of change of the derivative. For a position function the first derivative is velocity (how fast your position is changing) and the second derivative is acceleration (are you speeding up or slowing down).

In the example above the derivative is whether the economy is increasing or decreasing but the second derivative is whether that rate is speeding up or slowing down. In a graph the second derivative is the concavity so the graph of the economy would be decreasing but concave up, it is still going down, but less steeply with time.