A secant is a line that intersects a curve at two or more points. In geometry, it is often used in relation to circles, where a secant line crosses the circle at two distinct points. This concept helps in understanding the properties of circles and the relationships between angles and arcs. In trigonometry, the secant function, denoted as sec, is the reciprocal of the cosine function. It is defined as the ratio of the length of the hypotenuse to the length of the adjacent side in a right triangle. The secant function is important in various applications, including calculus and physics.