The spatial unit vectors for a 3 spatial dimension [x,y,z] vector are i^=[1,0,0], j^=[0,1,0], and k^=[0,0,1]. These are all said to be orthogonal to each other,

The spatial unit vectors for a 3 spatial dimension [x,y,z] vector are i^=[1,0,0], j^=[0,1,0], and k^=[0,0,1]. These are all said to be orthogonal to each other, which is a generalization of perpendicularity [1] to non-spatial vector spaces. As a lay person who is not familiar with the mathematics would recognize the term perpendicular, using that in the video is fine. [1] https://en.wikipedia.org/wiki/Orthogonality https://en.wikipedia.org/wiki/Orthogonality