A public IP address is an IP address that can be directly accessed over the Internet. A private IP address is an IP address on a local area network (LAN) in the public cloud system and cannot be routed through the Internet.
An EIP is a static, public IP address. You can bind an EIP to an ECS in your subnet to enable the ECS in your VPC to communicate with the Internet through a fixed public IP address.
Each EIP can be used by only one ECS at a time.