EIN (Employer Identification Number)

An Employer Identification Number identifies the company to the IRS. Despite the name, it has nothing to do with having employees. Every US company needs one to open a bank account, sign up with a payment processor or file a return.

The online application needs the responsible party's SSN or ITIN. A founder with neither applies on paper, using Form SS-4, by fax or through the IRS's international phone line, which is why the number takes weeks rather than minutes.