Adoption is the process by which persons take on the responsibilities of parenting for a child or children that may or may not be related to them biologically. In some cases, relatives adopt children within the family unit, in others; there is no biological relation between the children and the parents.
The legal process governing adoption severs the parental responsibilities of the biological parents and establishes a new legal relationship between the child and the new parents.
This is largely a matter of state law, but in general most states allow married persons and singles to adopt. Some states or foreign countries may have minimum age requirements.
This is also determined by state law, but in general, any person whose biological parents no longer have parent rights through consent for adoption, involuntary termination or death. In the last case, a child is considered an orphan and without parental care.