Open-mindedness is the name of that quality: the willingness to consider and accept other people’s ideas and opinions, rather than pushing them away at once. You talk about it as a thing a person shows, or a thing a class, a company, or a society values. “She showed open-mindedness” means she acted in that open way. It is the noun that belongs with the adjective open-minded; the idea is the same, only the shape of the word is different. You meet it a little more in essays, speeches, and careful praise than in quick chat. Though actually, students sometimes hunt for a second, secret sense — and there isn’t one. It is still that same willingness, named as a thing.