In this lecture, we will learn about the circle. A circle is a round, closed 2D shape where all points on its boundary are the same distance from the centre. This distance is called the radius. The diameter is twice the radius and passes through the centre. Important parts of a circle include the chord (a line joining two points on the circle), arc (part of the circumference), sector (slice of the circle), and segment (area between a chord and its arc). A tangent touches the circle at exactly one point, while a secant passes through two points on the circle. We can have special shapes like a semicircle (half of a circle) and a quarter circle (one-fourth). A circle also has infinite diameters and shows symmetry in all directions. Circles are everywhere — in wheels, coins, clocks, and nature.