Which of the following is considered taxable income?

Wages, bonuses, and commissions are considered taxable income because they represent direct compensation received by employees for their services. This income is subject to federal income tax, Social Security, and Medicare taxes, and is reported on an employee's W-2 form at the end of the year.

In contrast, health benefits received by employees are typically not taxable as income under specific provisions of the tax code. Reimbursements for work-related expenses are generally not considered taxable because they are compensatory in nature, intended to cover costs incurred during the performance of job duties. Similarly, employer contributions to retirement plans often come with tax advantages and are not taxed as income until withdrawn, typically during retirement. Hence, among all the options presented, wages, bonuses, and commissions are the only items classified wholly as taxable income in the current tax framework.