Category C visas are non-immigrant visas for people who are traveling to a country and have to pass through the US for a limited amount of time. This type of visa is valid if you are in the US and you need to change airports. Even if you do not have to change airports, you can still go outside of the airport with a transit visa.
If you are planning to stay more than 1 day in the US you will have to apply for another type of visa. Thus, other purposes such as visiting family or sightseeing are not possible with this visa. If you already own a visitor (B) visa, you can use this to transit the US.
When you might need a transit visa:
- When you are in a foreign country embarking on a cruise ship that will make a stop at a port in the US, without the intention of staying in the US
- When you are travelling to the US as a crewmember of an aircraft or ship to join one of these vehicles