Federal Tax Id Number (EIN)
This applies to all 50 states plus home and online businesses, as well as any other business. 
Also known as an irs number it is  a unique 9 digit number (ex. 12-3456789) that the Internal Revenue Service and other federal agencies use to identify your business for many tax purposes.
Corporations or LLCs, employers, and, in some states, those businesses that are also getting a Seller's Permit are required to obtain a Federal Tax Id (FEIN) and a Business License. You can use a federal tax id number as your business id number. Otherwise, you will need to use your social security number over the phone or the internet all the time for orders or other business identification reasons. And your don't want your social security out there if you want to protect your identity.
Employers, Partnerships & Corporations or LLCs.Fed Tax Id (1- 24 hours)
This applies to all 50 states plus home and online businesses, as well as any other business. 
There are 4 Business Tax ID Numbers. 
A federal tax ID number (Federal EIN), 
a State Employer (State EIN) Tax ID Number, 
a State Sales Tax ID Number ( seller's permit / wholesale license), and 
a Business Tax Registration ID (Business License).