A circle is the set of all points equal in distance from a center point. If you pinned a piece of yarn down, then tied a pencil to the other end of the yarn and pulled the pencil around, you'd roughly draw a circle.

Here are some more definitions that you need to know

• Chord: a line segment connecting two points on a circle.
• Diameter: the distance across the center of a circle.
• Radius: the distance from the center of a circle to a point on the circle.
• Secant: a line intersecting a circle at two points.
• Tangent: a line intersecting a circle at exactly one point.

All circles are similar, meaning that they have the same shape but may be different sizes.

We are not going to do any exercises with circles right now, but we will be working with them when we get into area and perimeter.