Launch control refers to a "two-step" revlimiter.
The way this works operationally is fairly simple - there is a lower Rev Limiter while the car is stationary, so that you can floor it without causing danger to the engine. Pop the clutch, the car starts moving and the low Rev Limiter is disabled, allowing you to drive the car normally.
The main point of Launch Control is to enable consistent launches by keeping the car at the same RPM each launch.