1. Combining masturbation and prayer, most commonly in the form of praying you don't get caught whacking off in a compromising position.
2. Worshiping God by joyously making use of the self-pleasuring equipment with which thou hast been blessed.
So this one time I was doing some serious masterpraytion over cousin Sophie's bikini photos on Facebook, cause God help me if I get caught whacking off to that.
Due to intense lack of funds, a mastercation is a "staycation" wherein the only planned activity for amusement is masturbation. Should only be attempted by the truly pathetic.
I signed up for Naughty America for three days for $1.95, so I think I'm going to take Monday off and have myself a little mastercation.