The rate of change of demand for a good with change in consumers incomes...more on the income effect
Normally the income elasticity of demand; that is, the elasticity of demand with respect to income.
When used without another referent, appears to mean 'of consumption'. That is for income I and consumption C: income elasticity = (I/C)*(dC/dI) In one paper estimates were shown of .2 to .6 for a random sample of industrialized country middle class people. For more details see elasticity. Source: labor; macro