No difference.
"Gross income" refers to income from all sources and not yet netted against adjustments or expenses.
"Total income" refers to income from all sources.
"Net income" is what you call it AFTER you've deducted all direct expenses/deductions.
(Some answers above are a bit off. In tax parlance, "EBIT" is what you call income before taxes. It stands for "earnings before income taxes".)
For your project, you can dazzle 'em if you know the official income tax formula for individuals per the Revenue Code:
Income (all sources)
less exclusions from income (like non-taxable interest and child support)
= Total income
Total income
less adjustments for A.G.I.
= adjusted gross income
Adjusted gross income
less standard or itemized deductions
less exemptions
= taxable income
Taxable income
less tax credits
plus other taxes (such as self-employment tax)
less refundable credits
less prepayments of income tax (such as from a W-2)
= tax due or refund due
