Arc :
Arc Part of the circumference
Semicircle :
Semicircle Half of a full circle
Centre :
Centre The point inside the circle which is equal distant from all points on the circle (equidistant).
Radius :
Radius An interval drawn from the centre of the circle to the circumference
Diameter :
Diameter An interval passing the centre, which divides the circle in half.
(diameter = 2 x radius)
Sector :
Sector An area cut off by two radii
Chord :
Chord An interval joining two points on the circumference, but not passing through the centre
Tangent :
Tangent A line on the exterior of the circle that touches the circumference at one point
Minor segment :
Minor segment The smaller of the two regions inside a circle bounded by the circle and a chord
Major segment :
Major segment The larger of the two regions inside a circle bounded by the circle and a chord