Device drivers are shared computer programs that provide an interface between the hardware devices and operating system or other higher level programs.
You need a specific software program to control each hardware device attached to the computer. It is very tedious to make any piece of hardware work. For example to write to a hard disk, you need to know the specific address available, wait till hard disk is ready to receive data and then feed it with data once it is ready. So instead of writing the same code for a device in multiple applications you share the code between applications. To ensure that the shared code is not compromised, you protect it from users and programs. Such a piece of code is called the device driver.
Device drivers are hardware dependent and operating system specific. They allow you to add and remove devices conveniently from your computer system without changing any of the applications using that device.
In a networked environment, the communication software or network operating system allows computers to communicate with each other. It enables sharing and transferring of data across the network. It controls network operations and manages network security.