The United States makes temporary visas – in technical language, nonimmigrant visas – available to a wide variety of people, from the tourist coming for a short stay to the worker who plans to stay for years at a time. What these visas have in common is that they come with, under the law, a limited possible duration and various limits and restrictions on what activities you can pursue in the United States on that visa. What’s more, they do not (except in rare circumstances) lead directly to a U.S. green card.
Many nonimmigrant visas allow their holder to apply for an extension of their stay, up to a certain maximum. However, if the visa holder stays in the United States beyond the time permitted time, this can lead to severe penalties and create problems for the person’s future immigration plans.