A closed adoption is a somewhat secretive adoption that is usually handled by a lawyer or an adoption agency. This usually involves either an unwed mother or a mother (or sometimes a couple) who feels that she cannot adequately care for a child. Frequently, (at least in the past) the biological mother was given none, or very limited, contact, with the newborn that is then presented to the adoptive parents. A birth certificate is prepared with the names of the adoptive parents on it and a judge signs off on the adoption paperwork. The records are then sealed and the child might go through life unaware that they he or she was adopted.
In our 21st century world, this type of adoption is not as common as it was in the past. There are a number of families who now opt for open adoption, not to mention movements by adoptees to be able to obtain at least the ethnic/medical histories of their birth parents. Also, modern DNA testing can put an adoptee in contact with members of their birth families, even without the availability of legal records.