For
Visitors on business (B-1)
Visitors for pleasure or medical treatment (B-2)

Requirements
1. Sufficient resources to visit the United States without working here
2. The demonstrable intention to return to your country after your visit

Length of stay
B-1: 3 months
B-2: 6 months

These are the normal stays given on entry, but it is possible to extend beyond these periods.

Notes
A citizen or legal permanent resident in the United States may be able to help a friend or family member obtain a visitor visa by extending a letter of invitation and an offer to support that person while in the United States.