Edge connector
From Sega Retro
An edge connector is a type of electrical connector for use with PC boards. They consist of a plastic "box" open on one side, with pins on either side of the longer edges, sprung to push into the middle of the open center. PC boards are then constructed with traces leading to the edge of the board, which are then slid into the edge connector. The edge connector is a money-saving device because it only requires a single connector, and they also tend to be fairly robust. For a time they were used in the vast majority of connectors found in computers, but modern computers have demanded many more pins than can easily be accommodated on the edge of a reasonable size board, and today more traditional male/female connectors are more common.