From Longman Dictionary of Contemporary Englishdiscretionary incomedisˌcretionary ˈincome noun [uncountable] the money remaining from your income after your bills have been paid, which can be spent on entertainment, holidays etc
Examples from the Corpus
discretionary income• As discretionary income moves from the young to the old, advertising will follow it.• They have a lot of flexible time and a lot have discretionary income.• I had a party today and used the discretionary income for it as a token of my approval.From Longman Business Dictionarydiscretionary incomedisˌcretionary ˈincome [uncountable]ECONOMICS income that you can spend on things that are not completely necessary for livingWhite-collar employees are usually furniture stores’ best customers because they have the most discretionary income. → income 