How can I name this 3D rotation

Question

First I would like to be clear: this is a noob question, I need a simple answer if such an answer exists.

In a three-dimentional space, how can I name this rotation?

See an animation

Let's assume X is red, Y is blue, Z is green. I need to know the direction of the rotation (+ or - 90°) and how can I name it: is it name depending on the Z axis which is the "static" axis of my box, or depending on the Y axis? I need to name this rotation for a physical sculpture documentation project.
I am sorry if I am a bit confused! Thanks for your help.

Answer 1

Use the right hand rule.

With the fingers of you right hand, follow the rotating object. Your thumb will be pointing in the direction of the axis you are revolving about. If it is pointing in the positive direction, your angle is positive. If it is pointing in the opposite direction, the angle is negative.