A more thorough explanation:

A nonimmigrant is a person who enters the United States for a temporary purpose, such as travel, work, or study. They do not plan to live in the United States permanently. To legally enter and stay in the United States for a limited period, a nonimmigrant must obtain a nonimmigrant visa. The type of visa and duration of stay depend on the purpose and activities of the nonimmigrant in the United States.

For example, a student from another country who wants to study in the United States would need a nonimmigrant student visa. A tourist visiting the United States for a short period would need a nonimmigrant tourist visa.

Nonimmigrants must follow the rules and regulations set forth in the Immigration and Nationality Act (INA). They cannot engage in activities that break the law or are unrelated to their principal purpose for being in the United States. If they do, they may be detained or deported.

Nonimmigrants must establish that they have a temporary basis for being in the United States and do not intend to stay permanently. They must prove this to the satisfaction of the consular officer when applying for a visa and the immigration officer when applying for admission to the United States.

For example, a person applying for a nonimmigrant visa to visit the United States must show that they have a permanent residence in their home country and intend to return there after their visit. If they cannot prove this, they may be denied a visa.

If a nonimmigrant violates their status or acts inconsistently with their nonimmigrant status within 90 days of admission, it is presumed that they willfully misrepresented their visa application purpose. This can result in detention or deportation.

For example, if a person enters the United States on a tourist visa but gets married to a United States citizen within 90 days of admission, it is presumed that they misrepresented their purpose for entering the United States and may be detained or deported.