Quoting from an FAA press release:
The Dominican Republic’s safety rating was raised from Category 2 to Category 1. A Category 1 rating means the country’s civil aviation authority complies with ICAO standards. A Category 2 rating means a country either lacks laws or regulations necessary to oversee air carriers in accordance with minimum international standards, or that its civil aviation authority — equivalent to the FAA for aviation safety matters — is deficient in one or more areas, such as technical expertise, trained personnel, recordkeeping or inspection procedures.[Photo Source]
As part of the FAA’s International Aviation Safety Assessment (IASA) program, the agency assesses the civil aviation authorities of all countries with air carriers that operate or might be authorized to fly to the United States and makes that information available to the public. The assessments determine whether or not foreign civil aviation authorities are meeting ICAO safety standards, not FAA regulations.
With the IASA Category 1 rating, Dominican carriers could apply to operate their own aircraft to the United States, which they currently do not. Countries with air carriers that fly to the United States must adhere to the safety standards of ICAO, the United Nations’ technical agency for aviation that establishes international standards and recommended practices for aircraft operations and maintenance.