A socket (jack) into which a cable is plugged. The word "port" implies an external connection to a peripheral device, whereas "slot" generally refers to an internal bus connection. For example, USB and Ethernet ports are sockets on the outside of the computer case that a cable plugs into. In contrast, PCI Express (PCIe) slots are sockets on the motherboard that expansion cards are inserted in. See
expansion card and
plugs and sockets.