Illegal aliens are individuals who are not citizens of the US, and who do not have the legal mandate to work or live in the country. The term dates back to 1798, when laws were being drawn up for alien and sedition acts. According to the American constitution, there is a clear distinction between aliens and immigrants, where immigrants are a subset of aliens. In some jurisdictions, illegal aliens are also known as unauthorized aliens.
Most illegal aliens in the country are present on account of work, and indulge in manual labor. A small minority are also known to deal with the sale and distribution of narcotics, though this represents an infinitesimally small proportion of illegal aliens. Despite being labelled as illegal, these individuals enjoy benefits including freedom of speech and expression, the right to an attorney when prosecuted.
Illegal aliens do not enjoy most of the benefits that a permanent resident or citizen would, including Social Security benefits (despite the fact that they contribute to the scheme) and federal safety-net programs such as Temporary Assistance for Needy Families and Supplemental Nutrition Assistance Program. However, most states bear the burden of caring for illegal aliens through programs such as Emergency Medicaid and Special Nutrition Program for Women, Infants and Children. These programs do not discriminate against the immigration status of an individual.
It is possible for an illegal immigrant to gain legal status such as temporary residency in the country. This involves filling all the applicable forms, and in some cases they may need to go to court as part of the process.