Supposed Origins
During a broadcast game on September 16, 2009, OGN commentator Um Jae Kyung (엄재경) briefly discussed the difference between a bunker rush and a "cheese" rush. According to his explanation, the term "cheese" originated from the word "cheater's" (words in Korean are sometimes shortened by the middle syllables, so 치터즈 [chi tuh zu] would become 치즈 [chi zu]). The strategy is characterized by, as opposed to a simple bunker rush, a practically unbeatable combination of most of the Terran's SCVs and a very quickly assembled group of marines. Because both Protoss and Zerg basic units are unranged, SCVs can effectively prevent the ranged marines from being destroyed by obstructing the path between the units, giving the marines a tremendous (and thus unfair) edge.
The usage of the term "cheese" has expanded to include most "all-in" strategies which involve a great sacrifice of economy, though some StarCraft communities use the term even more loosely to include mid-game strategies.
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