Disposable/Discretionary income

Another concept that is often confused with disposable income is discretionary income. This is equal to disposable income minus the cost of the fixed expenses of life (such as rent/mortgage, food, car payments, insurance, etc.). It is income that can be saved or spent on goods and services wanted, not needed. Disposable income is gross pay minus taxes and deductions. In other words, disposable income is the same as "net pay". Unfortunately, the definition of discretionary income is fuzzier than that of disposable income, making it harder to measure.
When applying for a loan or a mortgage, banks often refer to the customer's "disposable income" — based on the information here, the term they should be using is actually "discretionary income