The measurement and comparison of total growth per unit time is called as Absolute growth rate.
The growth of the given system per unit time expressed on a common basis is called as Relative growth rate.
Two leaves X and Y having different sizes show exact absolute increase in the area in the given time.
But, one of them has a much higher relative growth rate.
Consider, both the leaves have grown by 5 cm2 in a single day
The initial size of leaf X was 5 cm2, while that of leaf Y was 40 cm2.
Though the absolute growth rates both the leaves is the same, the relative growth rate in leaf X is faster.