That's right. According to the definition of semicircle in the first volume of ninth grade mathematics of Teaching Press, two endpoints of a circle with any diameter divide the circle into two arcs, and each arc is called semicircle. By definition, a semicircle is an arc. The semicircle should be separated from the semicircle: the semicircle is just an arc. It's a half circle. A semicircle consists of half a circle and a diameter, and the center of the circle is the center of its concentric circle. It has only one diameter, but there are countless radii and an axis of symmetry.