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.)