Over the back
From Computer History Wiki
Over the back or over the top are terms used to describe an alternative connectivity path between two more more boards plugged into a backplane; i.e. not using the bus carried by the backplane.
On the board edge opposite to the 'fingers' which plug into the backplane, a flat cable, or in some cases a small printed circuit board, with a pair of connectors plugs into Berg connector headers each board.
In a few cases (e.g. PDP-8 main memory), instead of headers, the back edge of the boards also has contact fingers, and what is effectively a small plug-on backplane is used to connect the cards.
