The Oxford dictionary states "income remaining after deduction of taxes and other mandatory charges, available to be spent or saved as one wishes."
Mandatory charges, to most people outside of this HN thread, are their bills and other common expenses. Mortgages, utilities, school and incomes taxes, etc are considered mandatory charges.
I'm not saying this to argue with you. Ya'll are welcome to interpret it how you like. But if you don't consider this perspective, you are going to misunderstand what other people intend to express when they use the term disposable income.
