A semi-open adoption falls somewhere in between an open and closed adoption.
Normally, semi-open adoptions have less direct communication between birth parents and adoptive parents. Although medical records are shared, no identifying information is shared. In semi-open adoptions, an adoption professional mediates between birth parents and adoptive parents. Like open adoptions, the birth parents have a lot of say in what their wishes are for potential adoptive parents. An adoption agency will guide the process of placement.
However, like open adoptions, no 2 semi-adoptions are the same. They can change over time. It gives you the freedom to be flexible on contact as it may change over time as you become more comfortable with the adoptive family/birth parent relationship.