Arc AXB along with radii AO and BO form a sector of a circle. A segment whose both the end points coincide or lie on the circumference of the circle, is known as the chord of a circle. In the circle shown above, only segment AB have both the end points lying on the circumference. Hence seg AB is a chord of a circle. For seg CD only one point C lies on the circumference, hence seg CD is not a chord of the circle.
Diameter is the largest chord of the circle.
A line, which intersects the circumference of the circle in two distinct points, is known as the secant of a circle. Line l does not intersect the circle hence it is not a secant. Lines m and n satisfy the condition of a secant as they are intersecting with the circle at two distinct points. Hence lines m and n are secants of the circle. It is worthwhile to note that the secant and the circle lie in the same plane.