Arcs are measured in degrees, like angles, and are classified in a similar way. There are minor arcs, major arcs, and semicircles. A minor arc measures between 0 and 180 degrees. A major arc is between 180 and 360 degrees. The semicircle is exactly 180 .
Arcs also have length.
Imagine placing a string along a portion of a circle, then picking it up and stretching it out, and measuring it. That is arc length. The sum of all the lengths of the non-overlapping arcs of a circle is called the circumference of that circle. This is the distance around the circle. Two circles that have the same center are called concentric circles.