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1.
The act of pleasuring oneself via the acquisition of a number in gaming, usually experience points or a level. Derived from the root terms 'the grind' (meaning job or repetitive process) and 'fap'
"Where was Jim at last night's LAN? Didn't he say he'd play CounterStrike with us?"

"No man, he was at home grindfapping to World of Warcraft"
by Eisen Feuer July 21, 2008