Meaning:

The total income of the nation is called national income. The aggregate economic performance of the whole economics is measured by the national income data. In fact national income data provides summary statement of a country aggregate economic activity. In real times national income is the flow of goods and services produced in an economy in a particular period of time, in short national income is the value of goods and services produce during a given counted  without duplication. The concepts of national income are GDP, NNP,GNP,PI,PDI.

Definition: according to National income committee of India 1948 “a national income is generally defined as some total of all the final goods and services produced in a country and net income from abroad in a year.

Concepts of national Income:

National income is expressed in different ways for example GDP, NDP, GNP, PI NNP and PDI.

1. GDP [ gross domestic product] :It is the aggregate value of final goods and services produced within the country during a year. In other word GDP the total money value of all final goods and services produced within the country by the national of the country and by the foreign national staying in the country during a year. The concept of GDP does not considered the value of goods and services produces with the nation working in foreign countries this means that it ignore the value of goods and services produce when non resident Indians working in foreign countries but consider the same when it is produced by foreigners working in India.
2. GNP [gross National product] : It is the aggregate money value of all finals goods and services produced by country in a year including net income from abroad. In other words  GNP measure the total money value of all final goods and services produced in a nation in a particular year + income earned by its not resident minus income earned by foreign staying in the country therefore the concept of GNP is much wider than the concept of GDP.
3. NNP[ Net National product] : GNP includes the value of total outputs of consumption goods and investment goods if we deduct depreciation cost from the total value of the goods and services we get net National product.
4.  PI [Personal income]: The national income of a country is distributed among the people of a country in the form of factor income. Therefore personal income is the part of national income of a country which is received by people or household. Social security contributions are payments made towards provident fund insurance, etc. transfer payments or payments made by a person, a firm government to another person, firm or government without expecting returns such as subsidies, old age pension, and scholarship are also considered as personal income.
5. PDI [ personal disposable income]: The whole of the personal income cannot be spent on consumption because taxes have to be paid on the income therefore the actual income which can be spent on consumption after detecting Direct taxes is disposable income It is the income which is at disposable of a person to spend as he wishes.

also read: explain the importance of estimation of national income.