Initial Side:The initial side of an angle is the ray that forms the starting point of the angle. It, along with the terminal side, defines the angle.
Angle:An angle is the figure formed by two rays, called the initial side and the terminal side, that share a common endpoint called the vertex.
Unit Circle:The unit circle is a circle with a radius of 1 unit, centered at the origin (0, 0) on the coordinate plane. It is used to represent and analyze the properties of angles.