It is the money value of all goods and services produced by a country in one accounting year. April 1 — March 31 is considered as one accounting year, or a financial year, in India.
A laborer working in an iron mill, a weaver spinning yarn, a farmer harvesting crop or a software engineer writing code all get paid at the end of the month; in some way, they convert their effort into money.
If you read something like the RBI expects India’s GDP to grow at 9% for fiscal (accounting) year 2008, it means that if India’s GDP in 2007 was Rs 100, this financial year it would be Rs 109.
Many people prefer to write national income instead of GDP.
Engineer's Finance 