Simple Definition:

Pi is a mathematical constant [a number that never changes] that represents the ratio [a comparison between the lengths] of a circle’s circumference to its diameter. It is approximately equal to 3.14159.

For example:

• If the circumference of a circle is 10 units, its diameter would be approximately 3.183 units.
• If the diameter of a circle is 5 units, its circumference would be approximately 15.707 units.

Very Simple Definition:

Pi is a special number that tells us how big a circle is. It helps us understand the distance around the edge of a circle compared to its width. It is about 3.14159.

For example:

• If a circle has a distance around the edge of 10 centimeters, this will be about 3.14159 times (pi times) bigger than the distance across it (around 3.183).