Define the American dream. What roles does the American dream play in the novel "Of Mice and Men"?

In the 1930's, the setting of Steinbeck's novella, Of Mice and Men, the American Dream was defined as the opportunity to work hard and achieve the socio-economic level that a person seeks.

According to James Truslow Adams, who coined the phrase "American Dream" in 1931, the American Dream is simply for everyone to have equal opportunity to live a better and more prosperous life. [https://www.reference.com/history/american-dream-1930s-809757d5533c5a2a]

For the bindle stiffs of Steinbeck's narrative, the American Dream is simply to have a home and a good job that will provide financial comfort. Financial security is certainly a real dream during the Depression when men must  try to find jobs and meals each day, sometimes, or at least move from job to job.
The dream of owning a small farm with rabbits and gardens is clearly the hope for security and happiness for Lennie and George. This hope that the American Dream offers is what keeps them and others working and saving money in the hope of attaining certain goals.