Inferior good

[1] There are many examples of inferior goods, including cheap cars, public transit options, payday lending, and inexpensive food.

[3][5] Inferiority, in this sense, is an observable fact relating to affordability rather than a statement about the quality of the good.

In some countries with less developed or poorly maintained railways this is reversed: trains are slower and cheaper than buses, so rail travel is an inferior good.

The potato, for example, generally conforms to the demand function of an inferior good in the Andean region where the crop originated.

People of higher incomes and/or those who have migrated to coastal areas are more likely to prefer other staples such as rice or wheat products as they can afford them.

However, in several countries of Asia, such as Bangladesh, potatoes are not an inferior good, but rather a relatively expensive source of calories and a high-prestige food, especially when eaten in the form of French fries by urban elites.

These effects describe and validate the movement of the demand curve in (independent) response to increasing income and relative cost of other goods.

[10] The increase in real income means consumers can afford a bundle of goods that give them higher utility.

[10] The income and substitution effects work in opposite directions for an inferior good.

It is usual to attribute Giffen's observation to the fact that in Ireland during the 19th century there was a rise in the price of potatoes.

The explanation follows that poor people were forced to reduce their consumption of meat and expensive items such as eggs.

Potatoes, still being the cheapest food, meant that poor people started consuming more even though its price was rising.

Good Y is a normal good since the amount purchased increases from Y1 to Y2 as the budget constraint shifts from BC1 to the higher income BC2. Good X is an inferior good since the amount bought decreases from X1 to X2 as income increases.
Engels curves showing income elasticity of demand (YED) of normal goods (comprising luxury (red) and necessity goods (yellow)), perfectly inelastic (green) and inferior goods (blue)
An item such as non-branded grocery products are common inferior goods. There is no set criteria of what constitutes an inferior good, but economists refer to an inferior good as any item preferred less when disposable consumer income increases.