If you have a small business (including a farm), you have the option of using your social security number or getting a federal employer identification number (EIN). If you pay W-2 employees, it is mandatory that you get an EIN. But even if you have no employees or only subcontractors, you have the option of requesting an EIN from the IRS. This allows you to use your EIN on certain tax paperwork instead of your personal social security number (such as a W-9 if someone needs to issue a 1099 for payments; or if you want to set up a separate bank account for the business.)
If you don't have an EIN but you are asked for your business tax number, use your social security number.
