Answer:
Form W-4 is Employee's Withholding Allowance Certificate. It's an IRS form that your employer gives you to complete for the employer's records. Allowable exemptions are the number of personal, dependable, and other exemptions that you claim on Form W-4. Your employer refers to the number of exemptions and your filing status to calculate income tax withholding from your earnings.
For more information, go to www.irs.gov/taxtopics. Select Topic 753: Form W-4 Employee's Withholding Allowance Certificate.
Also go to the Forms and Publications screen, www.irs.gov/formspubs. Select Publication Number to view/print Publication 505: Tax Withholding and Estimated Tax and Publication 919: How Do I Adjust My Tax Withholding?