I, too, have never seen the term "slot" used. It immediately brought to my mind the slot-like narrow feature in the lower section of the Mountaineer's Route chute (couloir) below the notch. Most people stay out of that, mostly staying to climber's left. But they could also avoid it by staying on the snow of the main chute.
The steep snow slope west of the 99 switchbacks is often called the chute, but it's to wide for a chute or couloir. I think of a gully as being a V-shaped stream-worn ravine.
> A reply was given with out asking if the questioner was referring to the Whitney Trail or the Mountaineer Route.
Nobody should offer an answer without first asking what "slot" they are talking about.