The nonimmigrant visa classification covers a broad range of visas used to enter the U.S. for work, pleasure or study. Some visas are considered 'dual intent'; you may attempt to obtain permanent residency (a green card) while under that classification. Most nonimmigrant visas, however, require you establish a nonimmigrant intent. This means you must demonstrate that you have a permanent residence in your home country that you have no intention of abandoning.
The duration of time you may spend in the U.S. can range from a few days to several years, depending on the type visa for which you are eligible. In most situations, your spouse and unmarried children under the age of 21 may accompany you on a derivative visa. In turn, your spouse and/or child may also be eligible for his/her own work permit or may be permitted to attend school in the U.S.
There is an alphabet of nonimmigrant visas. Some of the most popular are B2 (visitor); F1 (student); H-1B (specialty occupation); and J1 (exchange program/au pair).