The function \cos(\theta) represents the cosine of an angle \theta in a right triangle. It is defined as the ratio of the length of the adjacent side to the hypotenuse. In the unit circle, \cos(\theta) gives the x-coordinate of a point on the circle corresponding to the angle \theta. Cosine is one of the fundamental trigonometric functions, along with \sin(\theta) and \tan(\theta). It is widely used in various fields, including physics, engineering, and computer graphics, to model periodic phenomena and analyze waveforms.