There are a number of terms which are important to understand in studying population.
The crude birth rate is the number of births per 1000 people in a year.
The crude death rate is the number of deaths per 1000 people in a year.
The natural increase is the number of extra people (birth rate minus the death rate). This is usually given as a percentage.
The infant mortality rate is the annual number of deaths of infants less than one year old per 1,000 live births.