An arc is part of a circle. A circle is 360o, so an arc will be some portion of 360o. An arc is signified by its endpoints with a small arc symbol over the two endpoints and are classified according to their measure. A minor arc has a measure less than 180o. A major arc has a measure greater than 180o. If the arc's measure is exactly 180o, then it is called a semicircle.
The length of the arc of a circle will be explored in the measurement book of this unit.