Words I learned today

A Veblen good is a product whose demand curve shifts in proportion to its expense. The more it costs, the more desirable it becomes, such as the Hermes Birkin Bag, on which you can spend $124,750 (well, in theory you could).
A Giffen good is a product whose consumption increases as costs increase, defying typical supply-and-demand curves. Giffen goods are inferior goods whose demand disregards quality.
(Via the wonderful Felix Salmon, who actually used the latter term incorrectly–my Prada shoes are Veblen, not Giffen, goods, although I find them most desirable at 60% off.)