The sine function is a mathematical function that describes the relationship between the angle of a right triangle and the ratio of the length of the opposite side to the hypotenuse. It is commonly denoted as sin(θ), where θ represents the angle. The sine function is periodic, meaning it repeats its values in regular intervals, specifically every 360 degrees or 2π radians. In the context of the unit circle, the sine function can be visualized as the y-coordinate of a point on the circle corresponding to a given angle. The values of the sine function range from -1 to 1, making it useful in various applications, including trigonometry, physics, and engineering.