Is GDP and National Income the Same Thing?

[theBEAST]

I noticed in my textbook they said you can measure national income by measuring the GDP from either the expenditure or income side. So would this mean that national income and GDP have the same value?

 

[Matterwave]

Define National Income. Usually national income is just a vaguish word for "how much a country makes in a year" which is measured by concretely defined things such as GDP and GNP.