Circle Basics: Key Terms You Need to Know

Every circle has specific parts with precise names that you'll use constantly in maths. The radius is the distance from the centre to any point on the circle's edge - think of it as the circle's "arm reach."

The diameter is simply twice the radius, stretching right across the circle through its centre. Meanwhile, the circumference is the distance all the way around the circle's edge - like measuring a bicycle wheel's rim.

A chord is any straight line that connects two points on the circle, whilst a tangent touches the circle at exactly one point without crossing through it. Finally, an arc is just a curved section of the circumference, and a segment is the area between a chord and the arc it creates.

Quick Tip: Remember that radius × 2 = diameter, and every diameter is also a chord - but it's the longest chord possible!

The sector is like a slice of pizza - it's the area between two radii and includes the arc that connects them. These terms form the foundation for all circle calculations you'll encounter.