Originally Posted by robone
Its the speed after Kalman Filtering. And don't ask me what Kalman Filtering is
Wikipedia will give a better answer.
It is a mathematical model that will calculate the most statistically correct attitude solution based on the input from the sensor.
And to tie this into the previous GPS altitude vs. altimeter theme, both should be used by the Kalman filter to calculate altitude. Altimeter for short term changes, and GPS to compensate for long term changes (like weather changing the air pressure during flight). At least that is the common approach, but since YS-X6 is closed source one can only guess.