Luxury

Luxury goods are said to have high income elasticity of demand: as people become wealthier, they will buy more and more of the luxury good. This also means, however, that should there be a decline in income its demand will drop. Income elasticity of demand is not constant with respect to income, and may change sign at different levels of income. That is to say, a luxury good may become a normal good or even an inferior good at different income levels, e.g. a wealthy person stops buying increasing numbers of luxury cars for his automobile collection to start collecting airplanes (at such an income level, the luxury car would become an inferior good).
In economics, a luxury good is a good for which demand increases more than proportionally as income rises, in contrast to a "necessity good", for which demand increases less than proportionally as income rises.
Certain manufactured products attain the status of "luxury goods" due to their design, quality, durability or performance that are remarkably superior to the comparable substitutes. Thus, virtually every category of goods available on the market today includes a subset of similar products whose "luxury" is marked by better-quality components and materials, solid construction, stylish appearance, increased durability, better performance, advanced features, and so on.
As such, these luxury goods may retain or improve the basic functionality for which all items of a given category are originally designed.