Answer: The circumference of a circle is the edge or rim of a circle itself. It is the equivalent of 'perimeter' for a circle.
The glowing part in the circle above is the circumference.
Formula for circumference
You can use either of the formulas below to find the circumference . One formula use the radius of a circle; the other formula uses the diameter.
Formula using Diameter
$$ Circumference = \pi \cdot diameter $$
Formula using radius
$$ Circumference = 2\pi\cdot radius $$
**These two formulas are just two different ways of finding the same thing (circumference) because the diameter of a circle $$ =2 \cdot radius $$. So you can use whichever formula is more convenient. If you know a circle's radius, use the formula with radius ($$ 2 \cdot \pi \cdot radius $$) ; if you know the diameter, use the ($$ \pi \cdot diameter $$)