Arc (mathematical concept) generally refers to an arc. Circular arc is a Chinese vocabulary, and the pinyin is yuánhú. The part between any two points on a circle is called an arc. Maths is taught in junior high school and senior high school. Two endpoints of any diameter of a circle divide the circle into two arcs. Those larger than a semicircle are called optimal arcs, and those smaller than a semicircle are called suboptimal arcs.

A circle is a geometric figure. By definition, compasses are usually used to draw circles. The diameter and radius of the inner circle of the same circle are always the same, and the circle has countless radii and diameters. A circle is a figure with axial symmetry and central symmetry. The axis of symmetry is the straight line where the diameter lies. At the same time, the circle is a "positive infinite polygon" and "infinity" is just a concept. The more sides a polygon has, the closer its shape, perimeter and area are to a circle. So there is no real circle in the world, and the circle is actually just a conceptual figure.