Second derivative: p = price t = time dp = change in price dp/dt = change in price over time = inflation d^2p/dt^2 = change in change in price over t

Second derivative: p = price t = time dp = change in price dp/dt = change in price over time = inflation d^2p/dt^2 = change in change in price over time over time = change in inflation over time = what we are talking about