Define "Rich"

From Hal Varian's column in yesterday's NY Times:

After a detailed examination of the financial circumstances of people close to retirement, two economists, Stephen F. Venti of Dartmouth and David A. Wise of Harvard, concluded that the primary reason for differences in retirement assets was differences in propensities to save. It is not unusual to see low-income households with high savings rates holding more financial assets at retirement than high-income households who saved a smaller fraction of their income.

People often use the term "rich" as if the word had an unambiguous meaning. Venti and Wise show that high-income people and wealthy people are frequently different people.