Yes indeed Omar,
You rotate the UVs around the X-axis in the Mapping Node.
The same effect could be achieved by scaling the Y coordinates. Rotating around the X-axis 90°, would have the same result as scaling the Y to 0.
Every Y component (with the same X)) of the UVs is being mapped to the same value.
This only works because the UVs are 2 dimensional, but they live in a 3 dimensional world. Just like a Plane in Blender; you can look at a Plane from top orthographic view and rotate around the X-axis and it would look the same as scaling the Y.
Addendum:
This is not completely correct, the UVs do not have a Z component, so they would also be ‘flattened’ into the XY ‘plane’. So rotated around the X and having the Z component removed (or set to 0).
But incorporating that in the 3D picture would make it less clear, I think.
