What makes a supermodel ‘super’?

Say you're asked to name a supermodel. You probably wouldn't struggle to list Naomi Campbell or Linda Evangelista, or more recent inheritors of the title like Kendall Jenner, Adut Akech or Gigi and Bella Hadid. But now, imagine you're asked to define what makes Campbell and the Hadids "super," and others who walk the exact same runways just "models." Is it fame, or the fees they might command, or something more intangible?