"Networks are a system of connected data centers and servers that help power websites all over the internet. When you launch your applications inside of a network using a major cloud provider like Amazon, Google or Microsoft - you are essentially running your own virtual network inside of their data centers. This is known as a Virtual Private Cloud, and is simply a virtual network that you can operate, while a provider hosts the physical networking and appliances for you. Networks are the backbone of cloud applications and allow for proper IP traffic to flow in between systems so that they can all interoperate."
in other words
The system that connects everything.