Difference between socket.request.session.passport.user and socket.request.sessionID

I'm trying to creat a private tchat using socket.io, sessions and passport When I do a console.log(socket.request.session.passport.user) and a console.log(socket.request.sessionID). It gives me two different values, I don't understand why, because my purpose is to use a socket.broadcast.to(id).emit() in order to send private messages

so what is the difference between them?

via Meli