The Immigration and Nationality Act (INA) establishes the types of visas available for travel to the United States and what conditions must be met before an applicant can be issued a particular type of visa. The situations which make a visa applicant ineligible for a visa, called visa ineligibilities, are found in the INA, and other immigration laws. The INA also contains provisions for certain ineligible applicants to apply for waivers of their ineligibility.
When a visa applicant applies for a visa, a consular officer at a US embassy or consulate outside the United States determines whether the applicant is qualified, under all applicable US laws, to receive the particular visa applied for. Applicants found qualified are issued visas after all necessary processing is completed. However, when the consular officer determines that the applicant is ineligible to receive a visa, the visa application is denied. The applicant is informed verbally and in writing of the reason for denial based on the applicable section(s) of law.
If you are abroad, and a US consular officer has determined that you are ineligible for an immigrant visa or nonimmigrant visa because you are inadmissible to the United States, then you may be able to file an application for a waiver of inadmissibility.
If you have been removed from the United States and need permission to reapply, in addition to a waiver of inadmissibility, you may be able to seek permission to reapply for entry into the United States at the same time you request a waiver of your ground(s) of inadmissibility.