Employer Identification Number (EIN)
Definition: A 9-digit number obtained by a business with paid employees from the IRS. If you're a sole proprietorship, your EIN is your social security number. .
If you have one or more employees, you're required to withhold income tax and Social Security tax from each employee's paycheck and remit these amounts to the appropriate agency. To do so, you need to obtain an employer identification number from the IRS using Form SS-4; if your state has an income tax, you need to obtain a number from the state as well. Call your local IRS office, which will send you a copy of the form to file along with charts to determine payroll tax deductions, quarterly and annual forms, W-4 forms, tax-deposit forms, and a manual on filling out the forms. No advance fees or deposits are required.