Your visa stamp in your passport and your immigration status are not the same thing. It is important to understand the difference in order to fully understand how to maintain your legal right to stay in the U.S. It is very common for people to use the words "visa" and "immigration status" to mean the same thing, but this is incorrect. The following paragraphs explain the difference.
The visa stamp in your passport was obtained at a U.S. embassy or consulate abroad and is used to enter the U.S. The visa shows the latest date you may apply to enter the U.S. It does not show how long you may remain in this country. A valid visa is not necessary to remain in the U.S., so it is okay if your visa expires after you arrive. A valid visa is generally required to return to the U.S. after a trip abroad. If your visa stamp is expired and you will leave the U.S., you must reapply for a new visa to return. There are a few exceptions to this general rule, specifically for Canadian citizens and brief trips to bordering countries. If you are concerned about your visa expiration, contact Pam Barnum in the Immigration and Support Services office at 203-396-6400 or firstname.lastname@example.org.
After you are admitted to the U.S., an immigration status will be granted to you at the port of entry and will be shown on your I-94 card. Generally, your immigration status will be the same as the valid visa you used when you entered the U.S. However, if you are already in the U.S. and apply to the United States Citizenship and Immigration Service (USCIS) to change from your current status to another status, then your visa and immigration status will not be the same thing. Once you are inside the U.S., it is vital that you maintain your immigration status by pursuing your authorized activity.