Definition
Arc
An arc is a connected curved part of a circle or another curve between endpoints.
What it means
Mark two points on a circle, then travel along the curved boundary from one point to the other. That curved route is an arc. There are usually two ways around, so a diagram, direction, or words such as minor and major tell you which arc is meant.
Remember it
An arc follows the bend; a chord takes a straight shortcut.
Example
On a clock face, follow the circle’s boundary clockwise from 12 to 3. That route is a quarter-circle arc, covering one quarter of the circumference.
Watch for
The region inside the curve is not the arc, and a straight segment between the endpoints is not the arc.
Common mix-up
Arc length measures distance along the curve; it is not the straight distance between the endpoints.
Exact meaning
An arc is a connected portion of a curve between two endpoints. On a circle, two chosen points usually determine two possible arcs, so the intended route around the circumference may also need to be stated.