There are 2 common Cartesian coordinate systems in 3D software. Commonly referred to as CAD based and Character base. CAD based is technically z up y forward. If they are both positive then it is right hand orientation. If they are negative the it’s left hand orientation. Blender uses right hand orientation. Blender uses this because it was the most popular thanks to AutoCAD. Maya decided to follow Animation: Master and use character based system which is y up z forward and is also right hand orientation (positive). My understanding is that blenders Armature is based off of biped which was a popular plugin for 3DS back in the day, but I haven’t confirmed that.
