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In multiplayer games where players oppose each other based on some form of rating/ranking/tier system, tierslum or tierslumming, is the activity of finding ways to play in lower tiers than you belong, and hence dominating and gaining rewards or stats much quicker.
Uberganker1337 has a K/D of 4,2, but he got it tierslumming so it does not count.
by Tangouser July 24, 2011