The unit circle is a circle with a radius of one, centered at the origin of a coordinate plane. It is commonly used in trigonometry to define the sine, cosine, and tangent functions. The coordinates of any point on the unit circle can be expressed as (\cos \theta, \sin \theta), where \theta is the angle measured from the positive x-axis. In addition to its role in trigonometry, the unit circle helps visualize periodic functions and their properties. It provides a way to understand angles in both degrees and radians, making it easier to solve problems involving angles, triangles, and trigonometric identities.