What is COM Port? What is Serial Port? What is relation between COM and serial Port?

COM Port(Communication Port) is the original name given to serial ports on IBM compatible computers.
A serial port is asynchronous port on computer used to connect a serial device to computer capable of transmitting 1 bit at a time. It's basically a I/O port to get the data in and out of using computer. Normally every PC has one or 2 COM ports(serial ports).
A keyboard may be connected to COM1 and some other device may be connected to COM2.
Serial ports were mostly used for communication with RS-232, RS-485 system. A serial port is more than just a port, it converts data from parallel to serial and changes its electrical representation. Inside computer data flows in parallel( using many wires at a time) while serial flow is flow of bits over single wire.

Most of the electronics for serial port (convert parallel data to serial) is done in a computer chip that's known as UART.
Connectors for serial ports are of MALE and FEMALE type.

                                                       MALE JACK          Female JACK
Reference:
http://www.thaiio.com/serialportinfo.html