The line which touches the circle at only one point is known as tangent of the circle
A line drawn from external point of a circle which intersecting a point in circle and make 90degree angle and perpendicular to radius

A line touches the circle externally and make 90 degree with the center
A line touch the circle externally at one point
A line touching circle at only one point externaly.
A line meeting a circle only in one point is called tangent.
Tangent is a line which touch a circle only at one point