NDP stands for Net Domestic Product, whereas, NNP stands for Net National Product. NDP is an annual measure of the economic output of a nation that is adjusted to account for depreciation. NNP, on the other hand, is the market value of all the finished goods and services that are produced in a year, by citizens of a nation, living domestically and internationally.

Further reading:

• Measurements of National Income
• Indian Economy Notes for UPSC