What is a principle of democracy in which citizens agree that when differences of opinion arise they will abide by what most people want?

The principle of democracy you are referring to is known as the "majority rule." This concept holds that decisions should reflect the preferences of the majority of citizens while still respecting minority rights. It promotes fairness and stability in governance by ensuring that the views of the larger group are prioritized in decision-making, while also recognizing the importance of protecting the interests of individuals and minority groups.