I propose "band".
I am suggesting this as a new usage, as we do not seem to otherwise have a common word for this kind of thing.
I was coming at this question from the perspective of separating the row/column from the dividers separating them. The dividers, being narrow, are properly referred to as lines:
2: a straight or curved geometric element that is generated by a moving
point and that has extension only along the path of the point
In typical usage, a band is generally something thin and long, but generally indicates non-trivial thickness:
3: a strip serving to join or hold things together (belt, book band)
4: a thin flat encircling strip (strip of cloth, ring of elastic)
5a: strip (as of living tissue or rock) or a stripe (as on an animal) differentiable (as by color, texture, or structure) from the adjacent material or area
5b: a more or less well-defined range of wavelengths, frequencies, or energies
5c: range 7a
I particularly like the wavelength example; in science, we can refer to a spectral line (very narrow, specific wavelength emitted or absorbed) vs. a band, which indicates a wide range of wavelengths.
As I'm thinking about this, I'll also suggest for discussion "lane" or "track" as alternatives, though to me those both suggest motion along them.