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.
An unbroken part of a circle consisting of two endpoints on the circle and all the points between them is called a "chord." The chord connects the two endpoints, and the arc formed by the endpoints on the circle is the corresponding arc of the chord. Together, they define a segment of the circle's circumference.
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.