this ppt helps you to know about what is a circle , diameter , radius and chord

2. Circles

3. Nagavani

4.  Circle:- A round plane figure
whose boundary (the
circumference) consists of
points equidistant from a fixed
point (the centre).

5. Diameter :- The diameter of a
circle is any straight line segment that
passes through the center of
the circle and whose endpoints lie on
thecircle.
It can also be defined as the longest chord
of the circle.
Radius:- The radius of a circle is the
length of a line segment from its center
to its perimeter.

7. Chord :-A chord of a circle is a geometric
line segment whose endpoints both lie on
the circle