Counter transference is when you start responding back - ie playing the role that has been assigned you. So if you have ever seen a trainer get all 'school-marmy' on you,then they are probably in the grip of some counter-transference.
Why does this all matter to coach? Well if you are interested in keeping your communication clear and open then you can easily see how this stuff could murky the waters. So if your coachee suddenly starts putting you on a pedestal .. and you would quite like them to ... check out if there isn't something else going on and take it straight to supervision.