The growth rate of a value (GDP, turnover, wages, etc.) measures its change from one period to another (month, quarter, year). It is very generally expressed as a percentage.
For example the GDP growth rate between year n-1 and year n is given by the formula :
((GDPn- GDP-1) / GDPn-1) * 100
To make comparisons easier, quarterly growth rates are sometimes converted into annual rates.