H4 Visa

What is an H4 visa

An H4 visa is a visa issued by the U.S. Citizenship and Immigration Services (USCIS) to immediate family members (spouse and children under 21 years of age) of H visa holders (H-1A, H-1B, H-2A, H-2B, or H-3), so that they can legally stay in the US.
H4 visa holders (dependents) are not eligible to get a Social Security Number (SSN) and cannot be employed or start any business. They are eligible for driver's license, opening  bank accounts and get an Individual Taxpayer Identification Number (ITIN)  for  the US tax  filing purposes.

 Reference - http://en.wikipedia.org/wiki/H-4_visa