The ratio of the circumference of a circle to its diameter is a constant, known as π (pi). This means that no matter the size of the circle, if you measure its circumference (the distance around the circle) and divide that by its diameter (the distance across the circle through its center), you will always get the same value: π.
Approximately, π is equal to 3.14159, but it is an irrational number, which means it has an infinite number of non-repeating decimal places. The significance of this ratio stems from its fundamental properties in geometry and mathematics, and it appears in various equations and formulas involving circles.