a socket in this context means an open TCP connection between the server and the client
developer.mozilla.org/en-US/docs/Web/API/WebSocket
the advantage of this open connection is that your server and your client can communicate without having the overhead of an HTTP request.
so you can push messages from the client to the server and back. this messages are strings -> these string can be parsed to jsons, xmls, and other formats your client supports.
server gets an update -> pushes it to the clients.
does this explanation help ? This is really just a rough summary.