In case you are annoyed with math conventions like me you can find all of it explained in the euclideanspace site:
http://www.euclideanspace.com/maths/standards/index.htm
The ones that apply to Irrlicht are the DirectX ones if im not mistaken.
For Euler angles there are usualy lots of synonims to mess things up.
For DirectX the convention is that Y is up. For a pilot inside an airplane when he looks up he looks on the positive Y axis. Z runs along the airplane noose. The pilot is along the positive Z axis when looking forward inside it's airplane. When the pilot turns his head right he is looking towards the positive X axis.
Heading = Yaw = Azimuth = rotation around Y axis.
Pitch = Elevation = Altitude = rotation around the X axis.
Roll = Bank = Tilt = rotation around the Z axis.
For OpenGL is the same thing.
The order is also important so for an Euler angle the Heading is applied first, followed by the pitch and finnaly the roll. A different order produces different effects.