1. a social class existing beneath the usual socioeconomic scale, often concentrated in the inner cities and usually characterized by poverty, inadequate educational or vocational opportunities, high unemployment or chronic underemployment, violent crime, substance abuse, poor social services, and few community-supporting institutions.

2. broadly, any group without equal or direct access to the economic, educational, legal, medical, or other provisions of a society. For example, the term genetic underclass has been used to identify those who are classified as susceptible to a particular disease following genetic testing and who may as a result encounter discrimination by insurance companies or employers.