Definition: A circle is the locus of all points equidistant from a central point.
A circle is a type of line. Imagine a straight line segment that is bent around until its ends join. Then arrange that loop until it is exactly circular – that is, all points along that line are the same distance from a center point.
There is a difference between a circle and a disk. A circle is a line, and so, for example, has no area – just as a line has no area. A disk however is a round portion of a plane which has a circular outline. If you draw a circle on paper and cut it out, the round piece is a disk.
The circumference of a circle is the actual length around the circle which is equal to 360°. Pi (p) is the number needed to compute the circumference of the circle.
p is equal to 3.14. Pi is greek and has been around for over 2000 years!