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When a person or group of people smoke(s) a massive amount of marijuana in one sitting.
Stoner 1: "Homie, my friend and I had a master sesh last night. We smoked a quad between the two of us."
by JDRstoned August 17, 2009
the ultimate uninterruptable masturbation session
i locked the door, turned off the lights and threw on some quality internet porn. not even julius would be able to interrupt this mastersesh.

mastersesh? masterbest!
by yourname.001 February 18, 2011