Types of Goods (Normal/Inferior/Luxury/Necessity/Ordinary/Giffen)

Settings
x(p,w): Walrasian demand function of a good
p: Price of the good
w: Wealth (Income)

Normal Goods
∂x/∂w>0

Inferior Goods
∂x/∂w<0

Luxury Goods
(∂x/∂w)(w/x)>1

Necessity Goods
(∂x/∂w)(w/x)<1

Ordinary Goods
(∂x/∂p)<0

Giffen Goods
(∂x/∂p)>0

http://en.wikipedia.org/wiki/Good_%28economics%29