With respect to serial communication define the asynchronous communication.
Asynchronous implies "no synchronization", and therefore does not require sending and receiving idle characters. Though, the beginning and end of each byte of data should be identified by stop and start bits. The start bit shows while the data byte is about to begin and the stop bit signals while it ends. The need to send these additional two bits causes asynchronous communication to be slightly slower than synchronous still it has the advantage as the processor does not have to deal along with the additional idle characters.