" is a quadratic approximation of the original objective function in the tangent space of the feasible region."
-->
"is a natural approximation of the original objective function in the tangent space of a surface, this surface being the contour of the constraints at the current iterate."
https://github.com/ragonneau/phd-thesis/blob/da18a8c805481e89a267eed793067ab9410fc8a0/content/sqp.tex#L1081
" is a quadratic approximation of the original objective function in the tangent space of the feasible region." --> "is a natural approximation of the original objective function in the tangent space of a surface, this surface being the contour of the constraints at the current iterate."