In Euclidean geometry, an **arc** (symbol: **⌒**) is a connected subset of a differentiable curve. Arcs of lines are called segments or rays, depending whether they are bounded or not. A common curved example is an arc of a circle, called a **circular arc**. In a sphere (or a spheroid), an arc of a great circle (or a great ellipse) is called a **great arc**.

Every pair of distinct points on a circle determines two arcs. If the two points are not directly opposite each other, one of these arcs, the **minor arc**, will subtend an angle at the centre of the circle that is less than π radians (180 degrees), and the other arc, the **major arc**, will subtend an angle greater than π radians.