Expansion Card Slots
You might be familiar with the term PCI (Peripheral Component Interconnect). It is used to install additional components like Wireless adapters, graphics cards, etc. PCI is an expansion bus that is used to transfer data between the computer (i.e. CPU and RAM) and the connected peripheral device.
A bus can be understood as a path through which the data travels. The term refers to both the software and the hardware required to transfer data. A bus has two parts, the address bus which passes the information about where the data should go, and the data bus which carries the actual data to be transferred.
Modern motherboards include the PCIe (PCI Express) slots which are an upgrade over the conventional PCI and PCI-X expansion bus standards.