Pi is the ratio of the circumference of a circle to it's diameter

Pi represents a never ending number so to use it in maths we usually shorten the number to 3.14

For example: 3.14 ( Pi ) is used to work out area of a circle

• Circumference
  The distance around a circle is called the circumference
  
  
• Diameter
  The distance across a circle through the center is called the diameter
  
  
• Radius
  Half the distance across a circle from the center is called the radius