What does the .4 mean in 2.4 cups?

In the measurement of 2.4 cups, the ".4" represents four-tenths of a cup. This means that in addition to the two full cups, there is an additional amount equivalent to 0.4 of a cup. Specifically, 0.4 cups is equal to about 6.4 tablespoons or 1.9 fluid ounces.