I couldn't find this answer on Google because 'on' is such a common word.
In this node.js example:

conn.on('close', function() {

var pos =   connections.indexOf(conn);

    if (pos >= 0) {

        connections.splice(pos, 1);

    }

});

There is a .on method(?). What it does? It is a JavaScript method? Or it is something you only find in node? I'm kind of confused because I think I saw something like .on on jQuery. Is it similar to the jQuery .live event handler?

Can anyone explain this to me?