A single task or problem is divided into different parts and each part is done by different computers. They communicate and co-ordinate via network and perform the task as single entity. The user perceives it as a single system performing certain function.
The ultimate goal of distributed computing is to maximize performance by connecting users and IT resources in a cost-effective, transparent and reliable manner. It ensures fault tolerance and enables resource accessibility in the event that one of the components fails.
Automatic Teller Machine (ATM) system is an example of distributed system. Several teller machines are connected to bank database/central system to perform different banking transactions. World Wide Web, Scientific computing, multiplayer online games are examples of distributed computing systems.