Second mass distribution video may incorrectly say that inertia vectors are redundant

[moorepants]

A student asked me today why I said the inertia vectors are redundant in the video and we watched it. I think this was an incorrect statement about my misunderstanding years ago. I had it in my mind that the inertia vector contained all info on the inertia of an object, but it doesn't. You need at least 3 for a 3D object.

[Peter230655]

I checked the internet, but did not find a useful definition of inertia vector. I thought inertia in general is a 3 x 3 symmetric matrix (or tensor)?