Which of the following is NOT included in the taxable income reported on Form W-2?

The inclusion of different types of income on Form W-2 is based on whether that income is subject to taxation or not. Non-taxable benefits are amounts provided to employees that do not count as taxable income according to the IRS guidelines. These can include things like certain health benefits, life insurance premiums, or contributions to qualified retirement plans.

When it comes to the other options, they are typically included in the taxable income reported on Form W-2 because they reflect amounts that the employee must report for tax purposes. For instance, deferred compensation can be included in income when it is earned and vested, and the federal tax withheld is relevant for calculating overall tax obligations. Social Security tax withheld, while it is a deduction from an employee's paycheck, does not count as income itself, but it indicates what has been withheld for federal contributions.

Thus, non-taxable benefits stand out from the other items because they do not contribute to an employee's taxable income reported on Form W-2, which is why this is the correct answer.