What is mean by annual growth …

Annual Growth Rate of Population refers to the rate at which the number of individuals in a given popular increase over a year, expressed as a fraction of the initial popular of the previous years.

Other important explanation:

Growth of population or population growth refers to the change in the number of inhabitants of a country during a specific period of time, say during the last ten years.
It can be expressed in two ways:

Absolute Numbers. It is obtained by simply subtracting the earlier population from the later population. It is referred to as the ‘absolute increase’.
Annual Growth Rate. When the rate or pace of population is studied in per cent per annum. If increase is 2 per cent, i.e., there was an increase of two persons for every 100 persons in the base population. This is referred to as the annual growth rate.