IP address
An Internet Protocol address (IP address) is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication.
An IP address serves two principal functions: host or network interface identification and location addressing.
0.0.0.0
In the context of servers, 0.0.0.0 can mean "all IPv4 addresses on the local machine". If a host has two IP addresses, 192.168.1.1 and 10.1.2.1, and a server running on the host is configured to listen on 0.0.0.0, it will be reachable at both of those IP addresses.