In the United States, just because you are registered to do business in one state does not mean that you can legally do business in another state. If you want to transact any serious business in a state other than the state in which your Corporation or LLC was formed, you have to register with the state that is different from your incorporation/LLC state.

For example, if a California Corporation wants to do business in Nevada, then the California Corporation has to register with the state of Nevada. The state of Nevada considers the California Corporation to be a Foreign Corporation in Nevada.

The use of the term Foreign in this case refers specifically to individual US states. The US government, including the IRS, considers a Foreign Corporation to be a Corporation that is registered outside of the United States.