Semi-open adoption doesn't usually involve any post-placement, face-to-face visitation. The children involved don't normally have any direct communication with their birthparents. Like closed adoption, once a child reaches the age of majority in his or her state, they have the option of searching for or being searched for by their biological family. Unlike a closed adoption, those involved in a semi-open adoption usually have access to some basic information that can assist in the search process.
In an open adoption, as I define it, the adopters and the birthparents both know each other's full names, both first and last names. (It is not open if only one side has identifying information about the other.) They may agree to exchange photos and letters directly, without using the agency or attorney as a middleman. Sometimes a semi-open adoption later becomes an open adoption, if both parties decide that they want it that way.
Open adoption is a form of adoption in which the biological and adoptive families have access to varying degrees of each other's personal information and have an option of contact. While open adoption is a relatively new phenomenon in the west, it has been a traditional practice in many Asian societies, especially in South Asia, for many centuries. In Hindu society, for example, it is relatively common for a childless couple to adopt the second or later son of the husband's brother when the childless couple has limited hope of producing their own child.