Equation of a circle: The definition of a circle is a set of all points on a plane that are a fixed distance from a centre. The distance is called the radium. The equation of a circle is x2 + y2 = radius2.

Coordinate: A set of values that show an exact position on a graph. 

Tangent: A line that just touches a curve at a point.

Chord: A line segment connecting two points on a curve. (not the diameter)