Those are official definitions of the Statistics Division of the UN
(see Glossary at: http://unstats.un.org/unsd/sna1993/glossary.asp?letter=G
):
GDP - expenditure based:
GDP - expenditure based
Definition Expenditure-based GDP is total final expenditures at
purchasers? prices (including the f.o.b. value of exports of goods and
services), less the f.o.b. value of imports of goods and services.
Gross national product (GNP):
Gross national product (GNP)
Definition Gross national product (GNP) See ?Gross national income?.
Gross national income (GNI):
Gross national income (GNI)
Definition Gross national income (GNI) is GDP less net taxes on
production and imports, less compensation of employees and property
income payable to the rest of the world plus the corresponding items
receivable from the rest of the world (in other words, GDP less
primary incomes payable to non-resident units plus primary incomes
receivable from non-resident units); an alternative approach to
measuring GNI at market prices is as the aggregate value of the
balances of gross primary incomes for all sectors; (note that gross
national income is identical to gross national product (GNP) as
previously used in national accounts generally).
There are also definitions for:
GDP - income based
GDP - output based
GDP at market prices
Paulo Roberto de Almeida