This tag can be used to localize questions to United States. This can be used to help narrow the scope of your question or request information specifically involving this region. Examples include asking questions about where to buy merchandise, release dates, etc in the United States.
For example: Where can I buy the Full Metal Alchemist Manga?
This could be tagged with united-states to show that the user needs an answer that is relevant for the United States.
If the question you are asking is too broad, or if the information you are requesting would be more useful if it was specifically localized to the United States, then this tag is an appropriate addition to your question.