A tangent. And it does not need to be a circle - it can be any curve.
The tangent.
It is a straight line that touches the circle.
A tangent of a circle is a straight line that touches the circle at only one point.
A straight line from the center of a circle to the outer edge is called a radius.
Tangent
Tangent.
The tangent.
A tangent is always perpendicular to the radius of a circle. A radius is a straight line going from the center of the circle to the circumference (edge) of the circle. A tangent is a straight line outside the circle that touched the circle at one (and only one) point. When a tangent touches the outside edge of the circle at the same point where a radius touches the edge of the circle, the angle between the radius and tangent line is 90 degrees meaning they are perpendicular.
It is the tangent of the circle
It is a straight line that touches the circle.
A tangent of a circle is a straight line that touches the circle at only one point.
A straight line from the center of a circle to the outer edge is called a radius.
Tangent
The curved line that traces the boundary or perimeter of a circle is called the circumference. A straight line that touches the circle at just one point is called a tangent. See the related link, 'The Parts of the Circle', below this answer.
A tangent is a straight line that touches a circle's circumference at one point
It is the radius of a circle
A tangent of a circle is a straight line that touches the circle's circumference at just one point