Gross Domestic Product (GDP) is the total sum of the value of the final goods and services of the Primary, Secondary and Tertiary sectors of the economy of a country produced during a year.
The counting of the various goods and services for calculating GDP can he understood by the following example
Wheat and Hour are intermediate goods used for making final products like bread and biscuits. Intermediate products should not be counted in the figure of GDP. Biscuits and breads are the final products prepared using flour and other ingredients like sugar, salt, oil etc.
Only the final products are reaching the actual consumer. The value of the intermediate products is already counted in the final products and if this is again counted, it will lead to double counting, causing an error in the estimation of GDP.