Gyro sensor outputs


Dear All,
can anybody briefly describe what are the output variables of the 3axis Gyro sensor
(gyro.getAngle(i) and gyro.getGyroX) with respect to relevant physical quantities ?
In the documentation the explanations are rather poor. I also read most related topics on this forum: Many users claims they are Euler Angles (with zero chosen when gyro.begin() is invoked), but actually they are not, or at least not only, Euler Angles.(They might be Euler Angles at rest, but) how are they related to the acceleration?