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.

"For example, having an EIN for your business will allow you to use your EIN rather than your Social Security number when filling out Forms W-4 and W-9," Allec says. In general, an EIN can help ...