Sear
The surface that holds the cocked firing pin or striker until the trigger releases it, governing how clean and predictable the break feels.
The sear is the small mating surface inside the fire-control group that keeps the cocked firing pin under spring tension until you are ready to shoot. When you press the trigger, it pivots the sear out of engagement, the held energy is suddenly free, and the pin drives forward to strike the primer. The geometry and finish of that one contact patch decide much of what the shooter feels.
How the sear is shaped, polished, and angled sets the character of the break. A long or rough engagement surface produces drag and a heavy trigger pull, while a short, precisely honed sear releases crisply with very little movement. On a single-stage trigger the sear is the single point that has to let go cleanly, which is why quality fire-control groups treat sear engagement as the heart of the design.