A trade name is the official name under which an individual as a sole proprietor or a company chooses to do business. A trade name is commonly known as a doing business as (DBA) name. Registering a trade name legally is an important step in branding for a company, but it doesn't provide an unlimited brand name or legal protection for the use of the name.
As soon as you have a company, you must choose a trade name. This name can be descriptive, as long it does not cause confusion. If you want to protect your trade name, you need to use it in a demonstrable way, e.g. on your headed paper or website. Your customers or potential customers must know you by this name. You are not obliged to register the name in the Chamber of Commerce trade register. It is sensible, however, to first check whether the trade name that you want to use already exists.
What does it entail?
If you have a trade name, nobody else in the same sector may use the same or a very similar name, if use thereof could cause confusion. For instance, there would be confusion if your trade name could cause potential customers to mistake your name for that of your competitor, and so perhaps to do business with the competitor while thinking they are buying something from you.
The situation is different if the two companies are active in different sectors or in different geographical areas. In such a situation, the risk of confusion is smaller, even if the names are the same or very similar to each other.
If you have a website and, in theory, provide your services nationwide, it does not automatically follow that your trade name enjoys nationwide protection. If your customers mainly come from the region where your company is located, your trade name is protected in that area.
How long are trade name rights valid?
A trade name is valid for as long as it is demonstrably used. If the trade name is no longer being used, the right to it elapses.