The East Egg is where the "old money" individuals live in the novel "The Great Gatsby," whereas "new money" characters who were not born with their riches live in the West Egg. Therefore, this distinction represents a divide between the upper classes in the book.
This tension between the classes is a major theme of the novel. Characters such as Daisy and Tom, who gained their money via inheritance, tend to be more refined and respected. Throughout the course of the novel East Egg dwellers are also shown to be more self-involved and morally bankrupt. While West Egg inhabitants like Gatsby often got rich due to illegal activities, they tend to display more humanity.