Fictitious names are often required to be used by companies that operate under a publicly-known name but whose legal corporate entity is a different name.
One example might be if you were a sole proprietor Auto Detailer and your legal company entity was 'Clean Cars of Spotsylvania Corporation', but you wanted to now branch into cleaning houses as well. You might create a DBA/Fictitious Name/AKA of 'Cleaning Specialists of Virginia' and advertise under that name from now on in your coupon pack solicitations, and also advertise your car cleaning services under the regular corporate name in newspaper ads.
If you are proposing to use a name other than your full legal name for your business, and your business is not registered with the state of Virginia as a corporation or LLC, you are required to register that trade name with the Clerks office per state code §59.1-69 and §59.1-70. The Permit Center will not accept any permit applications without a copy of the approved registration form.