Definitions for "Tangent line"
A line that touches a circle at exactly one point and which makes a right angle with the circle's radius. For example, a circle that fills a square has four tangent points and the square's sides are tangent lines. An arc (curve) in a survey is part of a larger circle. One can construct tangent lines at the end points of the arc.
a line that is tangent to the graph of a specified function of one argument at a specified value of its argument
a line, which touches a given curve at a single point