The appeal to wealth fallacy is committed by any argument that assumes that someone or something is better simply because they are wealthier or more expensive. It is the opposite of the appeal to poverty.
In a society in which we often aspire to wealth, where wealth is held up as that to which we all aspire, it is easy to slip into thinking that everything that is associated with wealth is good. Rich people can be thought to deserve more respect than poorer people; more expensive goods can be thought to be better than less expensive goods solely because of their price.
This is a fallacy. Wealth need not be associated with all that is good, and all that is good need not be associated with wealth.
Examples
(1) My computer cost more than yours.
Therefore:
(2) My computer is better than yours.
(1) Warren is richer than Wayne.
Therefore:
(2) Warren will make a better dinner-guest than Wayne.
Each of these arguments takes an association with money to be a sign of superiority. They therefore both commit the appeal to wealth fallacy.