I cannot think what else I might add...
- Disposable income is net income. It's the amount left over after taxes.
- Discretionary income is the amount of net income remaining after all basic necessities are covered.
- Economists monitor these numbers at a macro level to see how consumers are saving, spending, and borrowing.
- An asset that is not being used as collateral on a loan and may therefore be sold or donated. In other words, an available asset is any asset with no restrictions on its use.
- See: Liquid asset.
You could refer to this money as discretionary income, which is the portion of your salary that doesn't go toward necessary bills such as taxes, housing, food, etc. You may also hear the term disposable income used synonymously, but apparently that refers to any income left after taxes, but still includes money that will be spent on necessary bills and cannot be spent "freely".
More general terms for money that isn't earmarked for anything in particular would be spending money or pocket money. These usually refer to not-very-large sums of money that can be spent as one pleases.