What is simplex communication

A communication network can provide many types of services such as simplex communication, Duplex communication, broadcast communication. The most basic type of communication is known as simplex communication. 

Simplex communication is one-directional communication that sends information in one direction only. 

For example :

In Radio communication Radio station usually sends signals to the audience but never receives signals from them. 

Paging system where messages are received, but not acknowledged.

Your keyboard to your CPU. The keyboard always sends characters to the CPU but the CPU never needs to send characters to the keyboard

In many cases, printers usually never send characters to computers but Computers almost always send characters to printers (there are exceptions, some printers do talk back). 

From the above example, we summarise that Simplex communication requires only one lane (in the case of serial).