Slot

A "slot" usually refers to the cartridge connector of cartridge systems, and is sometimes used to name 1-slot MVS boards.

Multi-slot boards use discrete or custom-made multiplexing chips such as NEO-244, NEO-253 and NEO-G0 to let the system ROM switch games.

Originally made by KEL, 4820 series (datasheet : https://www.kel.jp/files/topics/392_ext_19_en_0.pdf)