Huh. I'd always considered the definition of disposable income as the income that I would literally consider to be disposable, e.g. the money left over after I've covered everything I need (including housing, clothing, food and taxes) that I could set on fire and not change my current condition.
Per the wikipedia article of disposable income, I could afford a Ferrari (on a payment plan), but I would generally say I don't have the disposable income to afford a Ferrari because I still have to pay rent and feed myself.
Obviously the article defines that as discretionary income, I've always considered them to be equivalent terms.
> after I've covered everything I need (including housing, clothing, food and taxes) that I could set on fire and not change my current condition.
Housing and taxes make sense because they're generally inflexible costs, but how does clothing fit into this? Unless you're sewing smocks out of burlap, the majority of most people's clothing expenses is fully discretionary in every sense of the word (even including work clothes, for those unfortunate enough to have their employer force them to dress a certain way). That isn't to say it's a waste of money, but it's discretionary in the same way that eating at nice restaurants or going to concerts is: something you spend not to survive, but to improve your quality of life in some way.
These are standard economic terminology, not definitions made up by the article writer or wikipedia.. They're can be found in probably every introductory economics textbook from the past half century.
[1] https://en.wikipedia.org/wiki/Disposable_and_discretionary_i...