What is "old money"?

An important element of The Great Gatsby is the conflict between “old money” and “new money.” Gatsby, the self-made man, represents the nouveau riche, whereas the Buchanans represent the system of values perpetuated by generational wealth. Although both groups are in the same class, and equally wealthy, the differences between the groups have subtle social status issues.
People who are “new money” are seen by “old money” as gaudy, ostentatious, and overly extravagant. They are marked by excess and garishness. The wild parties that Jay Gatsby throws are indicative of this. On the other hand, “old money” folks think of themselves as elegant and refined.
The American Dream, an idea prevalent in all aspects of Fitzgerald’s novel, is based on “new money.” After all, it is conceptualized by the ability of the economically disadvantaged to move up.
The reality of this social mobility, however, is rather bleak. Gatsby, who gained his wealth through illegal means, is never fully accepted by people like the Buchanans. The separation and differences of West Egg (the new money area where Nick and Gatsby live) and East Egg (the location of the old aristocracy and gentry families) are symbolic of this divide.