# Circle Definitions

This section of Revision Maths defines many terms in relation to circles, including: Circumference, Diameter, Radius, Chord, Segment, Tangent, Point of contact, Arc, Angles on major and minor arcs, Angle of Centre and Sectors.

**Circumference: **The circumference of a circle is the distance around it.

**Diameter:** Any straight line that passes through the centre of the circle to two points on the perimeter.

**Radius:** Any straight line that originates at the centre of a circle and ends at the perimeter.

**Chord:** A straight line whose ends are on the perimeter of a circle. A diameter is the longest chord possible.

**Segment:** A part of the circle separated from the rest of a circle by a chord.

**Tangent: **A tangent to a circle is a straight line which touches the circle at only one point (so it does not cross the circle - it just touches it).

**Point of contact:** Where a tangent touches a circle.

**Arc:** A part of the curve along the perimeter of a circle.

**Angle on major arc: **The larger of 2 angles when a circle is split into 2 uneven parts. Greater than 180 degrees.

**Angle of centre:** An angle at the centre of a triangle between two lines that intersect with the perimeter.

**Angle at circumference on minor arc:** The smaller of 2 angles when a circle is split into 2 uneven parts. Less than 180 degrees.

**Sector:** A portion of a circle resembling a 'slice of pizza'.

More information on Circles can be found on the Circle Theorems page Here.