A doing business as, or DBA, number is a number that corresponds with any alternate names or titles under which a company operates. In most jurisdictions, companies are required to register any DBA names they have with the proper authorities for tax purposes.
To apply for a DBA number in the United States, businesses use the SS-4 application for an employer identification number, available from the IRS. This form must be filled out with information about the company in question, including the main type of business it engages and the number of people it employs. The company's DBA name must be entered on the form, as well as its legal name.