What is the defining characteristic of a tangent to a circle?

The defining characteristic of a tangent to a circle is that it intersects the circle in only one place. This single point of intersection, known as the point of tangency, means that the tangent line touches the circle but does not cross it.

Tangent lines are essential in geometry because they can provide information about the circle's properties, such as the radius drawn to the point of tangency being perpendicular to the tangent line. This relationship, while important, is a different aspect of tangents and does not change the fact that a tangent intersects the circle at precisely one point. Understanding this concept is vital for solving many geometric problems related to circles and tangents.