arc
A chord is the part of a circle defined by two endpoints.
The line passing through the center of a circle with two endpoints on the circle is the circle's diameter.
A chord is a line segment whose endpoints lie on a circle. A secant is a line (or line segment) that intersects a circle in two places, endpoints NOT on the circle.
a chord
Semi-circle
Two lines tangent to a circle at the endpoints of its diameter are parallel. See related link for proof.
A circle. has no endpoints.
It is a semicircular arc.
An arc is a part of a circle that is defined by its endpoints. It is a segment of the circumference of the circle.
Sector
They are two sections of the circumference of the circle.
Measure the distance between the two end points!