An arc is a part of a ring.

An arc is a term used in geometry to describe a portion or section of a curve. It is commonly associated with circles, but it can also refer to segments of other curved shapes such as ellipses or parabolas. In the context of this question, we will focus on arcs in relation to circles.

Definition of an Arc:
- An arc is a continuous portion of a circle's circumference or boundary.
- It is formed by connecting two endpoints on the circle with a curved line.

Understanding the Components of an Arc:
To fully comprehend what an arc is, it's important to understand its key components:

1. Endpoints: These are the two points on the circumference of the circle that define the arc. They are connected by the curved line.

2. Chord: The chord of an arc is the straight line segment that connects the endpoints of the arc. It is the shortest distance between the two endpoints.

3. Radius: The radius of a circle is the distance from the center of the circle to any point on its circumference. The radius also bisects the chord of the arc, dividing it into two equal parts.

4. Central Angle: The central angle is the angle formed by the two radii that extend from the center of the circle to the endpoints of the arc. It is measured in degrees and corresponds to the portion of the circle's total circumference that the arc represents.

5. Measure of an Arc: The measure of an arc is determined by the central angle it subtends. A full circle measures 360 degrees, so if an arc subtends a central angle of 60 degrees, its measure is 60 degrees.

Properties of an Arc:
- The measure of a minor arc is always less than 180 degrees.
- The measure of a major arc is always greater than 180 degrees.
- A semicircle is an arc that measures exactly 180 degrees.
- A central angle of 360 degrees corresponds to a complete circle and its arc is the full circumference of the circle.

Example:
For example, if we have a circle with a radius of 5 units, and we draw an arc subtending a central angle of 90 degrees, the measure of the arc would be 90 degrees. The arc itself would be a portion of the circumference of the circle, connecting two endpoints on the circle's boundary.

In conclusion, an arc is a part of a ring, specifically referring to a portion of a circle's circumference. Understanding the components and properties of an arc helps us analyze and solve geometric problems involving circles and curved shapes.