The Internal Revenue Service is only interested in your taxable gross income. It's what you have before claiming exemptions, deductions and credits. FICA taxable gross isn't different from this as much as it's a part of it. That term covers the portion of gross income subject to Social Security and Medicare taxes.
Gross and FICA Income Elements
Wages, tips and self-employment earnings are the most common taxable gross elements, but there are many more. Ordinary dividends, investment profits, pensions, unemployment benefits and alimony received count too. So do taxable interest earnings and the taxable portions of IRA distributions and Social Security benefits. FICA taxable gross includes only wages, salary, tips and self-employment income.