DBA stands for “doing business as,” which is a company name, also commonly called a “fictitious business name.”
When a sole proprietor operates a company using any name except his or her own given name, then the DBA or fictitious business name registration establishes the legal ownership to satisfy banks, local authorities, and customers.
So when you start the Acme Restaurant, unless you are named Acme, you need your DBA to open a bank account in that name, pay employees, and do business.
You can usually obtain this registration through the county government, and the cost is no more than a small registration fee plus a required newspaper ad, for a total of less than $100 in most states.
For more on the subject, check out: The Complete Guide to Registering Your Business Name.