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 circle can be expressed as (cos θ, sin θ), where θ is the angle measured from the positive x-axis. The Unit Circle helps visualize the relationships between angles and their corresponding trigonometric values. As the angle increases, the coordinates change, allowing for easy calculation of sine and cosine for various angles, including those beyond 90 degrees.