To shift from very high rpms in higher gear into lower gear, thus driving rpms even higher, way past redline. This leads to severe engine damage, since rev limiter cannot protect an engine in this situation.
A very costly maneuver, typically performed in street or drag racing when people shift from third into second instead of fourth.
I was at 6k in third, and then I did a moneyshift. Now it will cost me 2 grand to fix up the engine.