Socket
In plain terms
An endpoint for sending and receiving network data.
Going deeper
A socket combines an IP address and port to form a communication endpoint that programs use to exchange data over a network. It's the programming interface to networking.
Under the hood
TCP or UDP sockets; the OS abstraction apps use to read/write network streams.
Examples
TCP/UDP connections, network programming, WebSocket, client-server links.
Think of it like...
Like a specific phone jack you plug into to make a connection.