Toppling is one way to describe the way we create a turn, popularized by Tom Gellie++. The idea is based on using gravity and inertia to help move you efficiently inside and out of a turn as opposed to forcing the movements.
Topple: to (cause to) lose balance and fall down
For example, you can make a tree topple by changing its base or by using a lot of energy to push it over. Toppling is the intentional and controlled falling either sideways or forwards or backwards.
Towards the end of the turn, we are balanced on the outside ski, in equilibrium in relation to the forces acting on us (gravity, centripetal etc). Something needs to be done to disturb this balance and allow us to end the turn, setting things in motion for the next turn.
Effective ways to disturb the balance include late angulation (allow the upper body to move towards the new turn), flexing the outside leg (remove the support that keeps us balanced against the forces) which allows the body to move towards the downhill etc.
To support any turning, the skis must be on edge and the COM, the Center Of Mass, must be inside the arc of the skis, a concept is called Inclination of COM++. "Toppling" is an efficient way to get there, as the mass of the body must move lower and inside into the turn, to create the angles required to balance against the eventual forces of the turn.
Other elements that are important in the High-C, as we create the inclination at the top of the new turn, are Extending to maintain contact with the snow, Tipping the feet and ankles into the new turn and relaxation - a tense body does not allow an effective toppling.
Pull the inside boot up is how we allow the body to topple and create more angles.
Isn't toppling the thing that we experience when we properly release a turn by softening outside leg and let centripetal force to get upper body on the other side of the skis? HH has article 'Using the force' in ES2 book which describes this.
Here PL uses this term to describe how to change edges after flex to release: https://www.youtube.com/watch?v=QPycnnJqavg&t=11s&ab_channel=PaulLorenz