A Technical Rush is an unorthodox build which is highly specialised to a match-up, player or map. The purpose of a Technical Rush is to force your opponent to play in a specific, predictable way by presenting him with an unexpected situation. The rushing player can then control the game flow and take the win. The theory is that the rushed player makes a series of decisions, each of which is perfectly justifiable in that situation, but which as a whole put them at a significant disadvantage. It works because the rushing player is playing with the knowledge of the full strategy in mind whereas the rushed player is forced into making a number of short term, situational and often contradictory decisions.
Comparisons to Cheese builds
Although Technical Rushes rely on surprise and the predictability of the opponents' counter to be successful, they are very different to Cheese builds. While a Cheese relies on luck to be successful, such as an opponent being in a certain base site, opting for a certain build or forgetting a specific counter, a Technical Rush has no such requirements. It exploits the unfamiliarity of the opponent with the nuances of the build. If it is successful it means the rushed player lacked the foresight or experience to see the game as a whole.
The most well known user of Technical Rushes is Boxer. He spent much of his career inventing new ways to play maps, new styles to force his opponent to react to and inventing counter intuitive yet highly effective strategies. In this game against Hiya he did a counter intuitive and nonsensical strategy which left Hiya making a string of correct decisions and still finding himself considerably behind.
This game between Stork and fOrGG on Destination in the recent Lost Saga MSL demonstrated a highly effective map specific Technical Rush in which fOrGG was forced to choose between a fast expansion which would cost him the game to an Elevator or an All-in rush which was unlikely to work.