# Definition:Tangent/Geometry

## Definition

### Tangent Line

In the words of Euclid:

A straight line is said to touch a circle which, meeting the circle and being produced, does not cut the circle.

In the above diagram, the line is tangent to the circle at the point $C$.

### Tangent Circles

In the words of Euclid:

Circles are said to touch one another which, meeting one another, do not cut one another.

In the above diagram, the two circles are tangent to each other at the point $C$.