Definition - What does PCI Slot mean?
A Peripheral Component Interconnect (PCI) slot is a connecting apparatus for a 32-bit computer bus. These tools are built into the motherboards of computers and devices in order to allow for the addition of PCI devices like modems, network hardware or sound and video cards.
Techopedia explains PCI Slot
In older personal computers, users often took advantage of PCI slots to integrate relatively primitive modems as well as video and graphics capacity into the hardware setup, or to "expand computing." Some referred to these slots in the motherboard as connectors for internal devices, as opposed to external additions. Generally, these kinds of connections are not plug-and-play, but require the use of specific drivers for the central computing systems to recognize whatever is connected to the PCI slot.
As computing technology has evolved, in many cases the more sophisticated PCI express (PCI-E) slots have replaced the older PCI slots. However, many devices still have the ability to connect to peripherals through these kinds of ports and connections.