Who is a nonimmigrant person?

A quick search of the meaning of Nonimmigrant on USCIS.gov online dictionary (glossary) gives the following definition and explanation:

An alien who is admitted to the United States for a specific temporary period of time. There are clear conditions on their stay. There are a large variety of nonimmigrant categories, and each exists for a specific purpose and has specific terms and conditions. Nonimmigrant classifications include:

Foreign government officials;

Visitors for business and for pleasure;

Aliens in transit through the United States;

Treaty traders and investors;

Students;

International representatives;

Temporary workers and trainees;

Representatives of foreign information media;

Exchange visitors;

Fiancé(e)s of U.S. citizens;

Intracompany transferees;

NATO officials; and

Religious workers.

According to USCIS most nonimmigrants can be accompanied or joined by spouses and unmarried minor (or dependent) children.