A stall launch is when you receive multiple Kiss the Rails from the same rail. This is possible in certain scenarios if there is the right collision in front of a grindable rail. The collision pushes you back onto the rail, resulting in another Kiss the Rail, and this process repeats until either your speed or height is great enough to launch forward.
You can then chain frameboosts afterwards like normal, to further increase your speed.
Stall launches that generate high speeds in order to clip through walls may have differing performance between hardware and emulator.
Useful stall launches are known in Chuo Street, Kibogaoka Hill, and Bottom Point.