A backplane is similar to a personal computer's motherboard and sometimes a term improperly used to describe the computer's motherboard. The backplane is a printed circuit board containing connections (slots) for expansion boards and allows for communication between all connected boards.
An example of a backplane used with earlier computers was the NLX form factor, which had connections for expansion cards and a motherboard. Another place you may find a backplane is in a corporate network router, which is a large router that allows the use of expansion boards and modules for enhanced communication.
There are two types of backplane systems; an active backplane and passive backplane. With an active backplane the backplane contains the slots as well as the necessary circuitry to manage and control all the communication between the slots. However, a passive backplane has only the bus connectors and very little or no additional circuitry. In a passive backplane system all the communication is handled by one or more expansion boards that have been connected to the backplane.