A tangent is a straight line that touches a curve at a single point without crossing it. In mathematics, particularly in geometry, the tangent line represents the slope of the curve at that specific point. This concept is often used in calculus to analyze how functions behave locally. In the context of circles, a tangent line is perpendicular to the radius drawn to the point of tangency. The term "tangent" is also used in trigonometry, where it refers to the ratio of the opposite side to the adjacent side in a right triangle, often denoted as tan.