Explanation: A virtual private cloud (VPC) is a virtual network dedicated to your AWS account. It is logically isolated from other virtual networks in the AWS cloud. You can launch your AWS resources, such as Amazon EC2 instances, into your VPC. You can configure your VPC: you can select its IP ad-dress range, create subnets, and configure route tables, network gateways, and security settings. A subnet is a range of IP addresses in your VPC. You can launch AWS resources into a subnet that you select. Use a public subnet for resources that must be connected to the internet, and a private subnet for resources that won’t be connected to the Internet. If a subnet’s traffic is routed to an in-ternet gateway, the subnet is known as a public subnet. If a subnet doesn’t have a route to the Inter-net gateway, the subnet is known as a private subnet. If a subnet doesn’t have a route to the internet gateway, but has its traffic routed to a virtual private gateway, the subnet is known as a VPN-only subnet. Reference:
http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_Subnets.html