The function "cos(θ)" represents the cosine of an angle θ in a right triangle. It is defined as the ratio of the length of the adjacent side to the hypotenuse. In the context of the unit circle, where the radius is 1, cos(θ) gives the x-coordinate of a point on the circle corresponding to the angle θ measured from the positive x-axis. Cosine is a fundamental concept in trigonometry, often used in various fields such as physics, engineering, and computer graphics. It is periodic, with a period of 2π, meaning that cos(θ) repeats its values every 360 degrees.