DBA for business
A DBA ('Doing Business As', also referred to as 'trade name' or 'fictitious name') is used when you have a company such as an LLC or Corporation which wants to operate under multiple names, while using the same federal and state tax identification numbers for the business.
You do not have to have DBA's under your business, they are optional. For example, let's say you have a registered company named ABC, LLC, and you want to advertise and have a website with a different name. You would then file a DBA allowing your business to operate under multiple business names.