1. Plane-geometry:

In plane-geometry, a tangent to a circle is a line that intersects a circle at just one point. It touches the circle at that point of contact, but does not pass inside it.

2. Trigonometry:

In any right-angled triangle, the tangent of an angle is defined as the length of the side opposite the angle divided by the length of its adjacent side; $$\tan\theta=\frac{\text{opposite}}{\text{adjacent}}$$ , where 0°<θ<90°.