More common is probably the session Master. And I want to talk from my point of view as a slave a little bit about those Masters.
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A session Master is a 100% Master within a certain amount of time and period, or better said within a session. When he is in a session he is 100% top, dominant, sadistic etc. He likes to play with his slaves and uses them and does great things in a session. But before and after the session he is just a normal guy. He does not require, nor need or seek slave behavior from you. Most of my experiences I had was with session Masters, I think he is the most common type. Before a session you communicate a lot what can happen, what can be done etc. After the session you mostly talk about how the session was and reflect.