The most common information contained in your W-2 is your salary, the federal tax that has been withheld, the Social Security wages and the Medicare wages. Your W-2 also contains information about your employer and yourself as the employee. If you're wondering what is W-2, it can be described as a form containing your taxable wages and taxes that have been withheld during the year. Your W-2 form is used when you file your federal tax return, and may also apply for your state tax return.