It is a flat electronic board that contains the majority of the integrated circuits of your computer.
It contains enough connectors to allow for plugging of all other electrical components of the PC.
Some components of the motherboard are:
(i) The CPU or microprocessor
(ii) Random Access Memory
(iii) Expansion Slots
(iv) Ports and drive connectors
(v) Complementary Metal oxide semiconductor (Cmos battery)