It is a graph of the rate of change of the total number of deaths, in units deaths/day. I.e., the growth rate of the death count. The total number of deaths i

It is a graph of the rate of change of the total number of deaths, in units deaths/day. I.e., the growth rate of the death count. The total number of deaths is approximately the area under the curve, so if the curve stays constant as time goes on, the total area (number of deaths) increases linearly.