What's a "texel coordinate"? So I'm reading some Ray-Sphere interaction codes and in one there was "texCoord", which I think means "texel coordinate". However, what does this refer to "visually"?
It stands for texture coordinate.

It's a 2D value between 0 and 1 to indicate where in the texture to sample from for the color.

For sphere that means creating a map projection to map the curved surface to the flat plane, a simple option is to use the lat/long remapped to 0-1 though that gives awful distortion at the poles.