The ss command is used to dump socket statistics on Linux systems. It serves as a replacement for the netstat command and is often used for troubleshooting network problems.
What is a socket?
To make the best use of the ss command, it’s important to understand what a socket is. A socket is a type of pseudo file (i.e., not an actual file) that represents a network connection. A socket identifies both the remote host and the port that it connects to so that data can be sent between the systems. Sockets are similar to pipes except that pipes only facilitate connections between processes on the same system where sockets work on the same or different systems. Unlike pipes, sockets also provide bidirectional communication.
Source:: Network World – Linux