Any of the above. I really would like to use the word "john" just to feel all 1970s, Taxi Driver and shit, but just feels like I missed the moment for that
. I kind of like the word session, feels a little exotic. I usually just use the word "appointment" and "client", I have another small business and the terms are interchangeable, just works on a lot of different levels, especially if you are with friends or family who have no idea.