There is a thing inside the microcontroller called UART (Universal Asynchronous Receiver Transmitter). It takes a byte and splits it into bits. Then it sends (one bit at a time) it over a communication channel. Before serial communication, we used to use parallel communication by which we could send a number of bits for a character at once at the same time. You might have seen the parallel communication wire or port. A parallel communication wire looks as follows:

This is a pretty large port and it takes a large space on our computer, we Serial Communication was invented:

The serial communication can be done with any pin of the Arduino by using the SoftwareSerial library, or on pins 0 and 1 with the Serial class. We already used serial communication whenever we used the serial monitor, and also in the previous chapter while we worked with the GSM module. On our Arduino, the 0(Rx) and 1(Tx) pins are usually used for Serial Communication.